6 sci chp 7 solsn

 Class 6 Science Solutions 

      Chapter 7 Getting to Know Plants      

1. Correct the following statements and rewrite them in your notebook.
(a) Stem absorbs water and minerals from the soil.
(b) Leaves hold the plant upright.
(c) Roots conduct water to the leaves.
(d) The number of sepals and petals in a flower is always equal.
(e) If the sepals of a flower are joined together, its petals are also joined together,
(f) If the petals of a flower are joined together, then the pistil is joined to the petal.
Ans:
(a) Roots absorb water and minerals from the soil.
(b) Roots hold the plant upright.
(c) Stem conducts water to the leaves.
(d) The number of petals and sepals in a flower is usually equal.
(e) If the sepals of a flower are joined together, its petals are not necessarily joined together.

(f) If the petals of a flower are joined together, then the pistil is not necessarily joined to the petal. 

2. Draw (a) a leaf, (b) a tap root and (c) a flower, you have studied for Table 7.3 of the textbook.
Ans:

3. Can you find a plant in your house or in your neighbourhood which has a long but a weak stem? Write its name. In which category would you classify it?

Ans: Yes, we find a money plant in our house. It is a climber.

4. What is the function of a stem in a plant?

Ans: A stem performs following functions:

(i) The stem and its branches hold leaves to get maximum sunlight.

(ii) It transports water from roots to different parts of the plant.

(iii) It transports food from leaves to different parts of the plant.

(iv) It bears leaves, flowers and fruits.

5. Which of the following leaves have reticulate venation?

Wheat, tulsi, maize, grass, coriander (dhania), china rose.

Ans: Tulsi, china rose.

6. If a plant has fibrous root, what type of venation are its leaves likely to have?

Ans: Parallel venation.

7. If a plant has leaves with reticulate venation, what kind of roots will it have?

Ans:Tap root.

8. Is it possible for you to recognise the leaves without seeing them? How?

Ans: We cannot exactly recognise the leaves without seeing them. We may be able to have some idea by touching and smelling them.

9. Write the names of the parts of a flower in sequence, from outside to inside.

Ans: The names of various parts of a flower from outside to inside are:

(i) Sepals

(ii) Petals

(iii) Stamens

(iv) Pistil

10. Which of the following plants have you seen? Of those that you have seen, which one have flowers?

Grass, maize, wheat, chilli, tomato, tulsi, pipal, shisham, banyan, mango, jamun, guava, pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut

Ans:

11. Name the part of the plant which produces its food. Name this process.

Ans: Leaves produce food for the plant. This process is called photosynthesis.

12. In which part of a flower you are likely to find the ovary?

Ans: We find ovary in pistil. It is the lowermost part of the pistil.

13. Name two flowers, each with joined and separates sepals. 

Ans:

Flowers with joined sepals:

(i) Datura

(ii) Loki

Flowers with separate sepals:

(i) Gurhal

(ii) Mustard

10 sci chp 3 rvsn notes

   10 SCIENCE REVISION NOTES   

CHAPTER 3 ACIDS, BASES AND SALTS     

Elements are classified based on their properties as

→ Metals

→ Non-metals

→ Metalloids

Physical properties of Metals:

→ Metals are lustrous

→ All metals except mercury are hard and exist as solids at room temperature.

→ Metals are good conductors of heat and electricity.

→ Metals are malleable and ductile

→ Metals have high melting and boiling point.

→ Metals are sonorous and have high density

Exceptions:

→ Mercury is a metal which is liquid at room temperature

→ Lead and mercury are comparatively poor conductors of heat

→ Gallium and Caesium have very low melting point.

→ Alkali metals such as Sodium, Lithium and Potassium are soft and can be cut with a knife

→ The best conductors of heat are Silver and Copper.

Physical properties of Non-metals:

→ Non-metals are non-lustrous except lodine

→ Non-metals exists in solid, liquid and gaseous state.

→ Non-metals are non-malleable and non-ductile.

→ Non-metals have low melting and boiling points

→ Non-metals are non-conductors of electricity except Graphite.

→ Non-metals are generally not sonorous

→ Non-retals exhibits allotropic property. Diamond and graphite are allotropic forms of carbon

Exceptions:

→ Graphite is a non-metal but is a good conductor of electricity.

→ lodine is a non-metal but is lustrous.

→ Diamond is a non-metal but is the hardest substance known.

C'hemical properties of metals:

→ Reaction with Oxygen: When metals react with oxygen, metallic oxides are formed.

2Mg + O₂ → 2MgO (Magnesium oxide)

2Cu + O₂ → 2CuO (Copper oxide)

4Al + 3O₂ → 2A1₂O₃ (Aluminium oxide)

→ Amphoteric oxides: Metallic oxides which have both acidic and basic behaviour are called amphoteric oxides.

Examples: A1₂O₃ , ZnO

Al₂O₃ + 6HCI  → 2AICI₃ + 3H₂O

Al₂O₃+ 2NaOH → 2NaAIO₂ + H₂O

→ Some metallic oxides dissolve in water to form alkali

Na₂O(s) + H₂O(l)  → 2NaOH(aq)

K₂O(s) +H₂O(l) → 2KOH(aq)

→ Reaction with water:

Potassium and sodium react with water to liberate hydrogen gas

2Na + 2H₂O  2NaOH + H₂

2K + 2H₂O  2KOH+ H₂

Iron and aluminium react with steam to liberate hydrogen

2A1 + 3H₂O (steam) → Al₂O₃ + 3H₂

3Fe + 4H₂O (steam) → Fe₂O₃ +4H₂

Note: Hydrogen gas is not evolved when a metal reacts with nitric acid, because HNO₃ is a strong oxidising agent. It oxidises the hydrogen liberated to form water.

Reactivity of metals decreases in the order Mg > Al> Zn > Fe. This is assessed by the rate of formation of hydrogen bubbles.

→  Displacement reaction: The reactivity of metals is determined by displacement reactions

Example: Fe + CuSO₄ → FeSO₄ + Cu

Iron displaces copper from copper sulphate solution. Therefore iron is more reactive than copper.

Reactivity series: The reactivity series is a list of metals arranged in the order of their decreasing activities. This is determined by displacement reactions.

Most reactive → K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg. Ag, Au → Least

reactive

→ Reactions of metals with non-metals: Metals react with non-metals to form ionic compounds.

Na →Na⁺ + te,   Cl⁺ + e-  → CI^-

Na⁺ + CI^-   → NaCl

Properties of ionic compounds:

→ They are hard due to strong attractive forces between ions.

→ They have high melting and boiling points.

→ Electrovalent compounds are soluble in water.

→ They conduct electricity in their molten state or in aqueous solution

Occurrence and Extraction of metals:

Metals occur in nature in two forms:

→ Native form - Free state - Examples: Gold, silver, platinum and copper.

→ Combined form - Compound state - Examples: Sodium, potassium, magnesium, calcium, aluminium. zinc, iron, lead.

→ The Earth's crust is the chief source of metals. Sea water contains soluble salts of sodium and magnesium

→ Based on the reactivity series, metals are divided into

a] Metals of high reactivity. Examples: K, Na, Ca, Mg, Al,

b] Metals of medium reactivity. Examples: Zn, Fe, Pb.

c] Metals of low reactivity. Examples: Cu, Hg, Ag, Au.

Metallurgy: The process of extracting metals from their respective ores and purifying them is called metallurgy.

The steps involved in metallurgy are:

i] Concentration of ore.

ii] Reduction of the concentrated ore

il] Refining of the metals obtained

Minerals: The elements or compounds which occur naturally in the earth's crust are known as minerals.

Ores: Minerals which contain a very high percentage of a particular metal from which metal can be extracted profitably is called ore.

Examples

i] Ores of iron - Haematite, Magnetite

ii] Ores of copper - Chalcopyrites, Cuprite

iiil Ore of aluminium - Bauxite

Enrichment of ore: The ores of metals contain large amounts of impurities called gangue. The process of removing gangue from ore by different methods is called enrichment of ore.

Extraction of metals with low reactivity: These metals are extracted by converting them to their oxides and then reducing the oxides

Examples:

2HgS(s) + 3O₂ (g) -heat→  2HgO(s) + 2SO₂(g)

2HgO(s) -heat→  2Hg(s)+ O₂ (g)

2Cu₂S(s) + 3O₂(g) -heat→  2CuO(s) + 2SO₂(g)

2CuO (s) + Cu₂Ss -heat→  6Cu (s) + SO₂ (g)

Extraction of metals of medium reactivity

Roasting: The process of converting sulphide ores into is oxides called by heating  strongly in the presence of  excess of of air is called roasting.

Example: 2ZnS(s) + 3O₂(g)  -heat→ 2ZnO + 2SO₂.

Calcination: The process of converting carbonate ores into oxides by heating strongly in limited supply of air is known as calcination.

Example: ZnCO₃ (s) – heat→ ZnO (s) + CO(g)

The oxides of metal are reduced to metal by using a suitable reducing agent.

Example: ZnO(s) +C(s) -heat→ Zn (s) + CO(g)

Note: Obtaining metals from their oxides and compounds is a reduction process. Carbon is used as the reducing agent in extraction of metals. Some metals such as Na, Ca, and Al displace the metals of lower reactivity. They can also be used as reducing agents.

3MnO₂ (s) + 4A1 (s) → 3Mn (s) + 2A1₂O₃ (s) + Heat

Fe₂O₃(s) + 2Al(s)  → 2Fe (s) + Al₂O₃ (s) + Heat

The above reaction is used to join railway tracks or cracks of machine parts. This reaction is known as Thermit process.

Extraction of metals of high reactivity

Highly reactive metals are extracted by a method called electrolytic reduction of their oxides.

Example: Aluminium is obtained by electrolytic reduction of aluminium oxide.

Refining of metals: The process of purification of metals is called refining of metals. The best method of refining of metal is electrolytic refining Cu, Zn, Sn, Ni, Ag and Au are refined by this method.

Electrolytic refining of copper:

→ Acidified copper sulphate acts as electrolyte.

→ Impure copper plate acts as anode

→ Pure thin copper plate acts as cathode

→ Impurities that collect at the bottom of the tank are called anode mud.

Corrosion

The gradual process of eating away of metals by the reaction of atmospheric air and moisture with the metals is called corrosion.

Examples:

→ Rusting of iron - formation of hydrated ferric oxide.

→ Tarnishing of silver - formation of black coloured silver sulphide.

→ Green coating on copper due to formation of copper carbonate.

Prevention of corrosion

→ Galvanisation: Process of coating iron or steel objects with a thin layer of zinc is called galvanisation. This nis prevents rusting.

→ Alloying : Improving the properties of a metal by mixing with other metals.

→ Painting

→ Greasing

→ Tin plating

→ Chromium plating

Alloys: The homogeneous mixture of two or more metals or a metal with a non-metal is called an alloy.

Examples:

→ Brass - an alloy of copper and zinc (Cu, Zn).

→  Bronze - an alloy of copper and tin (Cu, Sn)

→  Solder - an alloy of lead and tin (Pb, Sn).

Note:

→  An alloy of metals in which mercury is one of the metals is called amalgam

→  Gold is very soft. Therefore some percentage of silver or copper is added to make it hard. This enables making of gold jewellery.

10 sci chp 2 revsn ntes

10 SCIENCE REVISION NOTES   

            CHAPTER 1 CHEMICAL REACTIONS AND EQUATIONS     

★ Based on chemical properties substances are classified as Acids, Bases and  Salts.

★ Acids prepared from minerals are called mineral acids

Examples: Hydrochloric acid - HCI,  Sulphuric acid - H₂SO_4, Nitric acid - HNO₃

★ Acids present in plants and animals are called organic acids

Examples: Lemon -citric acid, Tomato - oxalic acid, Tamarind - tartaric acid, Ants - Formic acid

★ Some other organic acids are:

Methanoic acid - CH₃COOH

Ethanoic acid - C₂H₅COOH

Benzoic acid - C₆H₅COOH

Formic acid - HCOOH

Indicators: An indicator is a dye that changes colour when it is put into an acid or a base

Types of indicators:

→ Natural indicators - Examples: litmus, turmeric, cabbage etc.

→ Synthetic indicators - Examples: phenolphthalein, methyl orange.

→  Olfactory indicators - Examples: Onion, vanilla, clove

→ Universal indicator - It is a mixture of several indicators

Properties of Acids:

→ Acids are sour to taste.

→ They turn blue litmus to red

→ Acids have hydrogen ions

→ They conduct electricity.

→ Acids react with bases to form salt and water.

→ Sulphuric acid reacts with zinc metal and liberates hydrogen gas.

When a candle is introduced into a soap bubble containing hydrogen gas, 'popping' sound is heard with a small explosion, indicating the gas liberated is hydrogen.

Zn(s)+H₂SO₄(aq) → ZnSO₄(aq) +H₂(g)

Note: Metals displace hydrogen from acids. All compounds which contain hydrogen are not acids

→ Hydrochloric acid reacts with metallic carbonate and metallic hydrogen carbonate to give carbon dioxide and sodium chloride.

Na₂CO₃ + 2HCI → 2NaCI + H₂O + CO₂

NaHCO₃ + HCI → NaCI + H₂O + CO₂

To know that CO, is liberated, pass the gas through lime water; where lime water turns milky.

Ca(OH)₂ (aq) + CO₂(g) → CaCO₃(s)+H₂O(l)

lf excess CO, is passed, then the following reaction takes place

CaCO₃(s) + H₂O (l) + CO₂(g) → Ca(HCO₃)₂

→ Reaction with metallic hydroxides:

2NaOH(aq) + H₂SO₄(q) → Na₂SO₄(aq) +2HO(l)

Ca(OH)₂(aq) + 2HCI(aq)  → CaCl₂(aq) + 2H₂O(l)

→ Neutralisation reaction: When an acid reacts with a base, salt and water are formed. This reaction is called neutralisation reaction.

NaOH (s) + HCI(aq) → NaCl(aq) + H2O(l)                                                                                                                 

Ca(OH)₂ + H₂SO₄  → CaSO₄ + 2H₂O                                                                                                                        

→ Conduction of electricity by acids:

When an acid dissolves in water it gives hydrogen (H⁺) ions or hydronium ions (H₃O⁺ ). Because of the formation of these ions acids conduct electricity in aqueous solution.

HCI  → H⁺ + CI^- (H⁺ hydrogen ion)

H⁺ + H₂O  → H₃O⁺ (H₃O⁺ hydronium ion)

Note:

→ Organic acids are non-conductors of electricity as they do not dissociate into ions

Examples: Formic acid - HCOOH, Methanoic acid - CH₃COOH, Ethanoic acid - C₂H₅COOH

→ Dilution of an acid is an exothermic reaction. Therefore acid is to be added slowly to water taken in a beaker with constant stirring. Suddenly adding acid to water causes splashing the acid which can cause burning of the skin In dilution of acids or bases H+ or OH- ions decrease per unit volume.

Properties of Bases:

→  Bases are bitter to taste.

→  Bases dissolve in water. A base which dissolves in water is called alkali.

→  Bases turn red litmus to blue.

→  Bases when dissolved in water give hydroxide ions (OH^- ions).

→ Bases react with acids to give salt and water.

2NaOH(aq) + H₂SO₄(aq) →  Na₂SO₄(aq)  + 2H₂O(l)  

KOH(aq) +HCI(aq) →   KCI (aq) + H₂O(l)  

→  Bases conduct electricity in their aqueous solution

pH Scale and pH Value:

→  The strength of an acid or a base is measured on a scale of numbers having values from 0 to 14. This is called pH scale and the numbers are called pH values.

→  pH has no units. It is a value which indicates how strong is an acid or a base.

→ Neutral substances or solutions have pH exactly 7

→ Acids have pH value less than 7.

→ Bases have pH value more than 7

→ A strong acid has a lower pH than a weak acid. A strong base has a higher pH than a weak base

→ Blood is slightly alkaline because occause its its pH pH is is 7.3.

→ pH value value of ofacia acid rain is less than 5.6.

→ Corrosion of teeth starts when pH of mouth is below 5.5 (tooth decay) on pain. Stinging the To sting hair of to counteract nettle counteract this, leaves the baking inject pain soda of methanoic (an the alkali) bee-sting. acid, is causing rubbed

→ Toothpastes which are alkaline are used to clean the teeth by neutralising the excess of acid in food to prevent tooth decay.

→ Antacids such as 'Milk of magnesia' are often used to neutralise excess of acid in our stomach

Salts

Common salt: Sodium chloride - NaCI

It is obtained by the evaporation of sea water. Common salt is used in obtaining various substances which are used in our daily life.

Caustic soda: Sodium hydroxide - NaOH

It is obtained by passing electricity through sodium chloride solution (brine). This process is called chloro-alkali process because of the formation of chlorine and sodium hydroxide, which is an alkali.

de-greasing

Uses: Used in making soaps, detergents, metals, paper manufacturing and making artificial fibres.

Bleaching powder: Calcium oxychloride CaOCl₂ 

It is produced by the action of chlorine on dry slaked lime.

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Uses: Used in bleaching cotton, wood pulp and clothes. Used as an oxidising agent in chemical industry and in chlorination of drinking water to make it free from germs.

Baking soda: Sodium hydrogen carbonate - NaHCO₃

It is produced by reacting sodium chloride with carbon dioxide and ammonia

NaCI + H₂O + CO₂ + NH₃ → NH₄CI+ NaHCO₃

When heated with water it produces carbon dioxide.

NaHCO₃ + H⁺ (from an acid) → CO₂ + H₂O + sodium salt of acid

Uses: CO₂  makes bread or cake to rise, making them soft and spongy. Therefore it is used in bakeries. It is used as an ingredient in antacids and soda-acid fire extinguishers

Note: NaHCO₃  + Tartaric acid is used as baking soda.

Washing soda: Sodium carbonate - Na₂CO₃ .10H₂O

Sodium 'carbonate is obtained by baking soda and by recrystallisation.

Na₂CO₃ + 10H₂O →  Na₂CO₃.10H₂O

Uses:

→ Used in the manufacturing of glass, soap and paper industry, manufacturing of Borax.

→ Used as cleaning agent at domestic level and removing hardness of water.

in on a v.C.) 

Water of crystallisation:

Water of crystallisation is the fixed number ber of of water molecules present in one formula unit of salt.

Example:

Copper sulphate - CuSO₄.5H₂O W.C. is 5.

Plaster of Paris 

Calcium sulphate hemihydrate- CaSO₄ ½ H₂O

It is a white powder obtained from heating gypsum at 373 K. It loses water molecule and gives plaster of paris.

CaSO₄.2H₂O  →  CaSO₄. ½ H₂O + 1 ½ H₂O

Uses: Used to support bone fractures in medicine. Used in making toys, decorative ceilings and for making smooth surfaces

Note: Plaster of Paris should be kept away from moisture because it sets into a hard solid mass.