Question

how many grams are represented by 1.45 moles of Koh? Determine your answer to the correct number of significant figures.

Answer 1

`\boxed {\boxed {\sf 81.4 \ g\ KOH}}`

Step-by-step explanation:

We are asked to convert 1.45 moles of potassium hydroxide (KOH) to grams.

1. Molar Mass

The molar mass is the mass in grams of 1 mole of a substance. The values are found on the Periodic Table. They are the same as the atomic masses but the units are grams per mole (g/mol) instead of atomic mass units (amu).

We have the compound KOH. Look up the molar masses of the individual elements.

• Potassium (K): 39.098 g/mol
• Oxygen (O): 15.999 g/mol
• Hydrogen (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 compound. We can simply add the molar masses.

• KOH: 39.098 + 15.999 + 1.008 =56.105 g/mol

2. Convert Moles to Grams

Based on the molar mass, there are 56.105 grams of KOH in 1 mole. Create a ratio using this information.

`\frac {56.105 \ g\ KOH}{ 1 \ mol \ KOH}`

We are converting 1.45 moles of KOH to grams, so we multiply by this value.

`1.45 \ mol \ KOH *\frac {56.105 \ g\ KOH}{ 1 \ mol \ KOH}`

The units of moles of KOH cancel.

`1.45\ *\frac {56.105 \ g\ KOH}{ 1 }`

`81.35225 \ g\ KOH`

3. Round

The original measurement of moles has 3 significant figures, so our answer must have the same.

For the number we calculated, that is the tenths place. The 5 in the hundredths place (81.35225) tells us to round the 3 up to a 4.

`81.4 \ g\ KOH`

Approximately 81.4 grams of potassium hydroxide are represented by 1.45 moles.