A sample of oxide iron weighing 2.40g was heated in a stream of hydrogen until it was completely converted to the metal. If the
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Answer:
Explanation:
To convert from moles to grams, the molar mass is used (mass of 1 mole). The values are the same as the atomic masses on the Periodic Table, but the units are grams per mole (g/mol) instead of atomic mass units.
<h3>1. Molar Mass</h3>We are given the compound sodium hydroxide (NaOH) and we need to look up the molar masses of the individual elements.
- Na: 22.9897693 g/mol
- O: 15.999 g/mol
- H: 1.008 g/mol
The formula for the compound has no subscripts, so there is 1 mole of each element in 1 mole of the substance. We can simply add the molar masses.
- NaOH: 22.9897693 + 15.999 + 1.008 = 39.9967693 g/mol
This means there are 39.9967693 grams of sodium hydroxide in 1 mole.
<h3>2. Convert Grams to Moles </h3>Use the molar mass we found as a ratio.
Since we are converting 17.6 grams of NaOH to moles, we multiply by this value.
Flip the ratio so the units of grams of NaOH cancel.
The original measurement of grams has 3 significant figures, so our answer must have the same. For the number we calculated, that is the thousandth place.
- 0.4400355406
The 0 in the ten thousandths place (in bold above) tells us to leave the 0 in the thousandth place.
17.6 grams of sodium hydroxide are equal to <u>0.440 moles of sodium hydroxide.</u>
The mass of piece of sterling silver jewelry is 33.24 g. It contains 92.5% silver Ag by mass. Since, sterling silver is an alloy of Ag-Cu thus, percentage of Cu will be:
% Cu=100-92.5=7.5%
Thus, mass of copper will be:
Molar mass of Cu is 63.546 g/mol, thus, number of moles of Cu can be calculated as follows:
Here, m is mass and M is molar mass.
Putting the values,
Now, in 1 mole of Cu there are thus, in 0.03923 mol, number of Cu atoms will be:
Thus, number of atoms of Cu will be.