8.1

What is counting by weighing?

A method of determining the number of objects by measuring their total mass and using their average mass.

Do objects need to have identical masses to be counted by weighing?

No. You only need to know their average mass.

What two things are needed to count atoms in a sample by weighing?

The mass of the sample and the average mass of the element.

What is average mass?

The total mass of a group of objects divided by the number of objects.

What is the formula for average mass?

Average mass = Total mass ÷ Number of objects.

How do you calculate the total mass of a group of objects?

Multiply the average mass of one object by the total number of objects.

What is the first step when calculating average mass?

Add the masses of all the objects.

What is the second step when calculating average mass?

Divide the total mass by the number of objects.

What is the formula for calculating the number of objects?

Number of objects = Total mass ÷ Average mass of one object.

What is the average mass of 10 jelly beans if their combined mass is 50.0 g?

5.0 g per jelly bean.

What is the average mass of one marble if 10 marbles weigh 37.60 g?

3.76 g per marble.

A pile of marbles weighs 394.80 g. If the average marble weighs 3.76 g, how many marbles are there?

105 marbles.

How do you calculate the number of marbles in a pile?

Divide the total mass of the pile by the average mass of one marble.

What is the formula for comparing different objects by weighing?

The ratio of the sample masses should equal the ratio of the masses of the individual components if the samples contain the same number of components.

What is the main idea of counting by weighing?

Objects can be counted using mass instead of counting each individual object.