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Mass calculations for SQA National 5 Chemistry

Mass calculations

This page covers the following topics:

1. Conservation of mass
2. Relative formula mass
3. Percentage mass

The principle of mass conservation states that for any system closed to any tranfer of matter or energy, the mass of they system must remain constant, meaning no quantity of atoms can be added or taken away. This means there must be equal atoms of each element on either side of an equation. This is true only in an enclosed system.

Conservation of mass

The relative formula mass of a compound is written Ar. To calculate the relative formula mass of a compound, add together the realtive atomic masses of each element within the compound.

Relative formula mass

Percentage mass is a way of representing the percentage of an element in a compound. Mass percentage is calculated by the mass of the element divided by the total mass of the compound.

Percentage mass

1

What is the percentage mass of oxygen in COโ‚‚?

(16 x 2) / 44 = 72.73%

What is the percentage mass of oxygen in COโ‚‚?

2

Work out the missing element X in compound Ca(XOโ‚ƒ)โ‚‚. It has a molecular mass of 164 g/mol.

40 + 2(X + 3 ร— 16) = 164
2X = 28
X = 14
X is N (nitrogen)

nitrogen

Work out the missing element X in compound Ca(XOโ‚ƒ)โ‚‚. It has a molecular mass of 164 g/mol.

3

What does the law of conservation of mass state?

No atoms are lost or made in a chemical reaction.

What does the law of conservation of mass state?

4

What is the relative formula mass of Cโ‚†Hโ‚โ‚‚Oโ‚†?

(12*6) + 12 + (16*6) = 180

What is the relative formula mass of Cโ‚†Hโ‚โ‚‚Oโ‚†?

5

What is the abbreviation for relative formula mass?

Ar

What is the abbreviation for relative formula mass?

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