2. What is baking powder? How does it make the cake soft and spongy?
3. When fresh milk is changed into curd will its pH value increase or decrease? Why?
4. Give Arrhenius definition of an acid and a base.
5. What happens chemically when quick lime is added to water?
6. Name the gas evolved when dilute HCL reacts with Sodium hydrogen carbonate. How is it
recognized?
7. How does the flow of acid rain water into a river make the survival of aquatic life in the river
difficult?
8. How is the pH of a solution of an acid influenced when it is diluted?
9. How does the pH of the solution change when a solution of base is diluted?
10. Arrange these in increasing order of their pH values- NaOH, blood, lemon juice.
11. Two solutions of A and B have pH values of 5 and 8. Which solution will be basic in
nature?
12. Why does tooth decay start when pH of mouth is lower than 5.5?
13. What would be the colour of litmus in a solution of sodium carbonate?
14. Name the products obtained when sodium hydrogen carbonate is heated. Write the chemical
equation for the same.
Answers
Answer:
2). Baking powder is a mixture of baking soda (NaHCO3) and an edible acid like tartaric acid. Baking powder on heating produces carbon dioxide gas which causes bread or cake to rise making it soft and spongy.
3). When milk is turned into curd then its pH value will decrease due to the production of lactic acid in curd which is acidic in nature. When milk turns into curd then it starts showing all properties of acid.
4). An Arrhenius acid is a substance that when added to water increases the concentration of H 1+ ions present. The chemical formulas of Arrhenius acids are written with the acidic hydrogens first. An Arrhenius base is a substance that when added to water increases the concentration of OH 1- ions present.
5). Chemically, quicklime or burnt lime is calcium oxide. When calcium oxide is added to water, it reacts to form calcium hydroxide (also called slaked lime). This reaction is highly exothermic and should not be tried without proper protection.
6). The gas evolved when sodium hydrogencarbonate reacts with dilute HCl is carbon dioxide. NaHCO 3 + HCl → NaCl + H 2O + CO 2. This gas is identified by passing it through lime water. When carbon dioxide gas is passed through lime water, it turns milky due to the formation of calcium carbonate which is insoluble in water.
7). Aquatic life sustains in optimal conditions required for their survival(pH,salinity,temperature etc). The environment where they live changes so some survive others die
Carbon dioxide gas is also easily soluble in water (directly from air) in water it forms carbonic acid, it also lowers the pH of water body along with acid rain (global warming).
Survivability of Aquatic flora and fauna is hugely affected by temperature and pH changes because they've evolved to live in water having pH 7 (certain temperature and salility) . Ex. Coral bleeching(corals die) because of incresed surface temperature of sea. There are some species able to tolerate these changes
8). When acid is diluted ,its pH will increase as pH of acid is less than 7. The pH of water is 7.
9). Dilution changes the pH value of an acid or a base toward 7. The pH value of a acidic solution increases with dilution and the pH values of a basic solution decreases with dilution. It is because by dilution the concentration of the H+ ions of an acid reduces and by dilution the concentration of the OH- ions of a base reduces.
10). lemon juice < blood< NaOH
11). Solution A is acidic and B is basic
12).Tooth decay starts when the pH of mouth is lower than 5.5 because:Tooth decays which are made of calcium phosphate are the hardest substance in the body.It does not dissolve in water.It gets corroded when the pH in the mouth is lower than 5.5.Acids are produced by the bacteria present in the mouth
13). We know that sodium carbonate is a basic salt. Hence, its aqueous solution will also be basic in nature. Since acids turn blue litmus red while bases turn red litmus blue, therefore when red litmus paper is dipped in sodium carbonate solution it will change to blue colour.
14). Sodium hydrogen carbonate (also known as
sodium bicarbonate or bicarbonate of soda) has
the chemical formula NaHCO3
. When it is heated
above about 80°C it begins to break down, forming
sodium carbonate, water and carbon dioxide. This
type of reaction is called a thermal decomposition.
2 NaHCO3 (s) Na2 CO3 (s) + H2O(g) + CO2 (g)