Q11 Name the acids present in the following foodstuffs which attribute to a sour taste to them- (a) Lemon juice (b)Vinegar (c) Vitamin C tablet (d)Tamarind (e) Sour milk
Q12 What does pH stand for? What does pH scale indicate?
Q13 Sweet tooth may lead to tooth decay. Explain, why? What is the role of tooth paste in preventing cavities
Q14 Write the names of five hydrated salts with their colours and formulae.
Q15 How are bases different from alkalis? Are all bases alkalies
Q16 What are strong acids and weak acids? Give two examples.
Q17 How will you test a gas which is liberated when hydrochloric acid reacts with an active metal?
Q18 Indicate with the help of a diagram the variation of pH with change in concentration of hydrogen ion and hydroxide ions showing Increase of acidic and basic nature. (i) Increase and decrease of H ion
Q19 What are indicators ? Give examples and their colour changes in different medium.
Q20 How will you prepare 100 times dilute solution from 1mL of concentrated sulphuric acid solution ? What precaution would you suggest and why?
Answers & Comments
Answer:
Lemon juice
pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water.
Remains of the sweets being taken may be present in between the teeth and bacteria acts on them at night producing an acid that causes decay of the enamel of the teeth. Toothpaste contains certain bases that help in destroying these bacteria and neutralising this acid, thereby preventing tooth decay.
a)Calcium sulphate dihydrate (CaSo4. 2H2O) . It is white in colour. b)copper sulphate pentahydrate (CuSo. 5HO). It is blue in colour. c)sodium carbonate decahydrate (Na2Co3. H2O). d)iron sulphate heptahydrate (FeSo4. 7H2O).e) magnesium sulphate heptahydrate (MgSo4. 7H2O).
Main difference is that bases that dissolve in water are called alkalis and bases that don't dissolve in water are only bases not alkalis, so we can say all bases are not alkali but all alkalis are bases. Bases and alkalis are typically metal oxides, metal hydroxides, metal carbonates and carbonates of molten hydrogen.
Strong acid: An acid which dissociates completely in water and produces a large amount of hydrogen ions. e.g., HCl. Weak acid: An acid which dissociates partially in water and produces a small amount of hydrogen ions. e.g., CH3COOH.