Science ( Common acids and alkalis (all chapters) )

Question 1

1 Acids have a ____ taste
2 Alkalis are slippery and some of them have a _____ taste.
3 Red cabbage leaves and red rose petals contain ____ which show different _____
in acidic and alkaline solutions. They can be used as ______ to distinguish between
acids and alkalis.
4 Acids turn blue litmus paper ______. Alkalis turn red litmus paper ____.

Answer 1

1 sour
2 bitter
3 pigment, colors, indicators
4 red, blue

Question 2

T or F
1 Sodium hydroxide solution is an alkali commonly used in the lab.
2 Many food contain acids or alkalis.
3 After handling acids or alkalis in the lab, we should pour the waste solution into the
sink.
4 All plant extracts can be used as acid-alkali indicators.
5 Litmus is an acid-alkali indicator commonly used in the lab.
6 There are three kinds of litmus, blue litmus, red litmus and purple litmus.

Answer 2

1 T
2 T
3 F
4 F
5 T
6 F

Question 3

Which of the following contain acid?
(1) Lemon
(2) Soft drink
(3) Baking soda

Answer 3

(1) and (2)

Question 4

Which of the following are precedures to do if dilute acid is splashed onto our hands?
(1) Report to the teacher immediately
(2) Wash the affected area under running water immediately
(3) Go to the hospital for treatment immediatetly

Answer 4

(1) and (2)

Question 5

Which of the following turn red litmus paper blue?
(1) Vinegar
(2) Lemon juice
(3) Glass cleaner

Answer 5

(3)

Question 6

Should oven cleaner come into contact with our skin?

Answer 6

No, since its has high levels of alkaline which may be corrosive or irritant.

Question 7

What should we do if oven cleaner gets into our eye?

Answer 7

We should wash the eye with plenty of water. If the accident is serious, go to the hospital for treatment immediately.

Question 8

What are three commonly used acids in the lab?

Answer 8

Hydrochloric acid, sulphuric acid, nitric acid

Question 9

What are three commonly used alkalis in the lab?

Answer 9

Sodium hydroxide solution, Calcium hydroxide solution, Ammonia solution

Question 10

What safety precautions should we take when handling acids or alkalis?

Answer 10

• Read the hazard warning symbols on the bottles of chemicals and identify the risks of
  handling them
• Wear safety specticles
• Wear a lab coact and disposable gloves when necessary to avoid direct contact with
  acids or alkalis
• Never taste acids or alkalis
• When working with acids or alkaline solution, fill no more than 1/3 of the container
• Do not mix acid or alkalis with other chemicals without getting approval from the
  teacher
• Pour the waste solutions into suitable waste bottles. Do not pour them into the sink
• Wash hands throughly after handling acids or alkalis

Question 11

What should we do if acids or alkalis come in contact with our body?

Answer 11

• We should keep calm and report it to the teacher at once
  –>Wash the affected area under running water immediately for atleast 10 mins
  –>If the eye is affected, wash it with an eye wash bottle immediately
  –>* Carefully remove clothes that have been contaminated

Question 12

1 In general, pH value ranges from 0 -14. This range is known as the ______.
2 Acidic substances have pH values ____ than 7. Alkaline substances have pH
values______ than 7.
3 A ______ is an electronic instrument used to measure the pH of solutions.

Answer 12

1 pH scale
2 lower, higher
3 pH meter

Question 13

T or F
1 We can use litmus paper to compare the acidity of different solutions.
2 We can use universal indicator or pH paper to distinguish between acids and alkalis.
3 Using universal indicator to measure the pH of solution is more accurate and precise
than using a pH meter

Answer 13

1 F
2 T
3 F

Question 14

Match the following
A Universal indicator i Mixture of several indicators
B pH meter ii Kind of natural indicators
C Litmus iii Needs calibration before measuring the pH of solutions

Answer 14

A i
B iii
c ii

Question 15

Which of the following has a pH value close to 7?
1 Sulphuric Acid
2 Milk
3 Bleach
4 Cola

Answer 15

2 Milk

Question 16

Which of the following orders correctly arranges the substances from decreasing pH?
1 Orange juice>Coffee>Egg white>Baking soda solution
2 Coffee>Orange juice>Baking soda solution>Egg white
3 Baking soda solution>Egg white>Coffee>Orange juice
4 Egg white>coffee>Baking soda solution>Orange juice

Answer 16

3

Question 17

Which of the following is used to find out of the pH of a solution?
(1) Universal indicator
(2) Litmus paper
(3) pH paper
(4) pH meter

Answer 17

(1) (2) and (3)

Question 18

When a drop of lemon juice is added to pH paper, the paper turns
(A) Violet
(B) Blue
(C) Green
(D) Red

Answer 18

(D)

Question 19

Can you find the pH value of soy sauce using pH paper? If not suggest a way to find the pH value.

Answer 19

No because the pH paper is masked by the color of the soy sauce.
Use a pH meter.

Question 20

What are the advantages and disadventages of using universal indicator? ( compared to pH meter )

Answer 20

Advantages
* Convenient: Calibration is not needed
* Less solution is needed for measurement
Disadvantages
* Measuremnt is less accurate and precise
* Bit suitable for dark-colored solutions

Question 21

What are the advantages and disadventages of using pH meter?( compared to universal indicator )

Answer 21

Advantages
* Measurement is more accurate and precise
* Suitable for solutions of any colors
Disadvantages
* Calibration is needed
* More solutions is needed for measurements

Question 22

1 When an acid mixes with an alkali, a reacton called ______ occurs. This reaction can be
represented with the word equation:
acid + alkali = ___+___
2 In neutralization, the mass of reactants and products is _______.
3 Antacid is ____. It helps neutralize excess acid in the stomach, thereby relieving pain.

Answer 22

1 neutralization, water, salt
2 conserved
3 alkaline

Question 23

T or F
1 Whenever we mix an acid and an alkali together, the pH of the resulting must be 7.
2 If precipitates are formed in neutralization, the mass of the products will be larger
than that of the reactants.
3 Toothpaste can neutralize acids in the mouth, thereby preventing tooth decay.
4 Sometimes farmers add lime to soil to lower soil pH

Answer 23

1 F
2 F
3 T
4 F

Question 24

When an acid is added to a beaker of alkali, what happens to the solution solution?
(A) The resulting solution turns red
(B) The resulting solution turns blue
(C) The pH of the resulting solution increases
(D) The pH of the resultin solutions decreases

Answer 24

(D)

Question 25

John adds 5cm3 of dilute sulphuric solution into a test tube containing 5 cm3 of dilute barium hydroxide solution. After 10 mins of waiting, what does John observe?

Answer 25

White precipitates are formed in the test tube.

Question 26

If the soil of a farm is 5.2pH, and the farmer wants to grow maizes(suitable soil is 6-7pH) in the farm, what should he do?

Answer 26

Add lime to the soil.Lime is alkaline. It can raise the soil pH.

Question 27

1 _______ + Hydrochloric acid –> Sodium chloride + Water
2 Potassium hydroxide + Nitric acid—-> ______ + Water
3 Sodium hydroxide + ________ —> Sodium sulphate + water

Answer 27

1 Sodium hydroxide
2 Potassium nitrate
3 Sulphuric acid

Question 28

alGive daily examples of neutralization.

Answer 28

• Brushing teeth with toothpaste
  –> Toothpaste is slightly alkaline. It neutralizes acids in the mouth and helps prevent
  tooth decay.
• Treating stomach ache with antacid
  –> Antacid is alkaline. it helps neutralize excess acid in the stomach and relieves pain
• Regulating soil pH
  –> Lime is alkaline. It can be added to acidic soil to neutralize acids in the soil.
• Treating insect stings and bites
  –> Wasp stings are alkaline. Vinegar can be used to neutralize the alkali in wasp
  stings.
  –> Bee stings and ant bites are acidic. Baking soda can be used to neutralize acids in
  the stings or the bites.
• Treating chemical waste
  –> To reduce pollution caused by chemical waste containing acids or alkalis, the
  waste can be neutralized with the use of suitable acids or alkalis before
  discharging.