A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
NaCl
HCl
LiCl
KCl
The solution contains HCl.
Give two important uses of washing soda and baking soda.
What is a neutralization reaction? Give two examples.
Plaster of Paris should be stored in a moisture-proof container. Explain why?
A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Leaves of the sensitive plant move very quickly in response to ‘touch’. How is this stimulus of touch communicated and explain how the movement takes place?
Read the following sources of loan carefully and choose the correct option related to formal sources of credit:
(i) Commercial Bank
(ii) Landlords
(iii) Government
(iv) Money Lende
Acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. Base is an ion or molecule capable of accepting a hydrogen ion from acid.
| Physical Properties | ACIDS | BASES |
| Taste | Sour | Bitter |
| Colour on Litmus paper | Turns blue litmus red | Turns red litmus blue |
| Ions produced on dissociation | H+ | OH- |
| pH | <7 (less than 7) | >7 (more than 7) |
| Strong acids | HCl, HNO3, H2SO4 | NaOH, KOH |
| Weak Acids | CH3COOH, H3PO4, H2CO3 | NH4OH |
| Type of Reaction | Acid | Bases |
| Reaction with Metals | Acid + Metal → Salt + Hydrogen gas (H2) E.g., Zn(s)+ dil. H2SO4 → ZnSO4 (Zinc Sulphate) + H2 | Base + Metal → Salt + Hydrogen gas (H2) E.g., 2NaOH +Zn → Na2ZnO2 (Sodium zincate) + H2 |
| Reaction with hydrogen carbonates (bicarbonate) and carbonates | Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water E.g., HCl+NaOH → NaCl+ H2O 2. Na2CO3+ 2 HCl(aq) →2NaCl(aq)+ H2O(l) + CO2(g) 3. Na2CO3+ 2H2SO4(aq) →2Na2SO4(aq)+ H2O(l) + CO2(g) 4. NaHCO3+ HCl → NaCl+ H2O+ CO2 | Base+ Carbonate/ bicarbonate → No reaction |
| Neutralisation Reaction | Base + Acid → Salt + Water E.g., NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) | Base + Acid → Salt + Water E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l) |
| Reaction with Oxides | Metal oxide + Acid → Salt + Water E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l) | Non- Metallic oxide + Base → Salt + Water E.g., Ca(OH)2+ CO2 → CaCO3+ H2O |
| Dissolution in Water | Acid gives H+ ions in water. E.g., HCl → H+ + Cl- HCl + H2O → H3O+ + Cl– | Base gives OH- ions in water. |
Read more on Acids, Bases and Salts