An empty beaker has a mass of 251.70 g. When water is added to the beaker, the combined mass is 268.309 g. What is the mass of the water in grams?

Answer 1

Hi Anna!

This is a method of weighing called "weighing by difference". In weighing by difference, the weight of the material (in this case, water) is equal to the difference between the two weights of the beaker before and after the water was added.

What this looks like mathematically is:

(Weight of the beaker + water) = (weight of the empty beaker) + (weight of water)

If we rearrange that, we get the "difference" and thus can solve for the weight of water:

(Weight of water) = (weight of the beaker + water) - (weight of the empty beaker)

Let's apply this to your problem!

Givens:

Weight of empty beaker = 251.70 g

Weight of beaker + water = 268.309 g

Calculations:

Weight of water = (weight of the beaker + water) - (weight of the empty beaker)

Weight of water = 268.309 g - 251.70 g

Weight of water = 16.609 g

Now, let's talk sig figs.

When adding or subtracting, we base our significant figures on the least number of decimal places. The weight of the beaker with the water (268.309) has three decimal places while the weight of the beaker without water (251.70) has two decimal places.

Therefore, our final answer will have two decimal places: 16.61 g!

Hope this helps! Feel free to contact me if you have anymore chemistry questions. :)

Answer 2

Simply subtract the mass of the empty beaker from the final total mass of the beaker + the water to get the mass of the water.

Answer 3

Let's write down some data:

1. mass empty beaker = 251.70g
2. mass beaker + water = 268.309 g

What is the question asking for?

What is the mass of the water?

Looks like this is just a sig figs question.

Here's the rules:

When adding or subtracting, round to the fewer number of decimal places:

The mass of water is just the difference in the two masses given; the mass increases due to the water, therefore:

mass beaker with water = mass beaker + mass water

Fill in the values:

268.309g = 241.70g + x

x = 268.309g - 241.70g

exact answer:

x=26.609 g

Significant figures rule: When adding or subtracting, round to the fewer number of decimal places.

One value has two decimal places. One value has three decimal places. Therefore, round to two decimal places:

Underline the first two decimal places:

x=26.609 g

Look at the third decimal place (the 9).

Does the third decimal place indicate that the second decimal place should round up? ...... Yes, because 9 is greater than or equal to 5, so the 0 should be round up to a 1. Therefore:

x=26.609 g=26.61 g