7th grade chemical reactions, acids and bases

Question 1

When 100 g of calcium carbonate is heated, it forms 56 g of calcium oxide and 44 g of carbon dioxide. What mass of carbon dioxide forms from 5 g of calcium carbonate, in g?

Answer g

Question 2

Who is often credited with showing that mass is conserved by careful weighing in sealed vessels?

• A. Dmitri Mendeleev
• B. Marie Curie
• C. Isaac Newton
• D. Antoine Lavoisier

Question 3

A solution has a pH of 4. Is it acidic, neutral or alkaline (basic)?

• A. acid
• B. neutral
• C. alkali (base)

Question 4

In a sealed flask, 38 g of substance A reacts completely with 21 g of substance B. 7 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 5

Complete the word equation: copper + oxygen → ___

• A. carbon dioxide
• B. copper chloride
• C. copper carbonate
• D. copper oxide

Question 6

Universal indicator results: pure water pH 7, vinegar pH 3, milk pH 6, soapy water pH 10. Which is the most alkaline?

• A. milk
• B. pure water
• C. vinegar
• D. soapy water

Question 7

Universal indicator turns red in a solution. What does this tell you?

• A. It is pure water
• B. It is neutral
• C. It is a strong alkali
• D. It is a strong acid

Question 8

A solution has a pH of 6. What colour will universal indicator turn?

• A. green
• B. purple
• C. blue
• D. orange or yellow

Question 9

Complete the word equation: copper + oxygen → ?

Answer 

Question 10

Firefighters cut a firebreak (a strip with no trees) in front of a wildfire. Which side of the fire triangle does this remove?

• A. heat
• B. fuel
• C. water
• D. oxygen

Question 11

Why does a candle under a glass jar go out?

• A. The wax turns into water
• B. The jar gets too heavy
• C. The oxygen inside is used up
• D. Glass puts out flames

Question 12

Why is limestone (calcium carbonate) heated in kilns?

• A. to turn it into gold
• B. to make oxygen
• C. to make it heavier
• D. to make quicklime (calcium oxide) for cement and building

Question 13

Word equations: which statement is NOT true?

• A. Incomplete combustion can produce carbon monoxide, a poisonous gas.
• B. Combustion is a reaction with oxygen.
• C. Reactants are written on the left of the arrow.
• D. Products are the substances you start with.

Question 14

Phenolphthalein is added to sodium hydroxide solution. What colour does it go?

• A. colourless
• B. yellow
• C. pink
• D. blue

Question 15

Acids and alkalis: which statement is NOT true?

• A. Acids have a pH below 7.
• B. Strong acids and alkalis can be corrosive, so eye protection is needed.
• C. Alkalis have a pH below 7.
• D. Pure water has a pH of 7.

Question 16

Magnesium carbonate is heated strongly and breaks down. What are the products?

• A. magnesium oxide + carbon dioxide
• B. magnesium + oxygen + carbon
• C. magnesium + carbon dioxide
• D. magnesium oxide + oxygen