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Question: In a sample of 35.0 g hydrogen sulphide, how many moles are contained? A) 1.03 mol B) 2.06 mol ...

In a sample of 35.0 g hydrogen sulphide, how many moles are contained?
A) 1.03 mol
B) 2.06 mol
C) 6.18 mol
D) 9.45 mol
E) 11.3 mol

Explanation

Solution

Chemical formula of hydrogen sulphide is H2S{H_2}S. To calculate number of moles in given 35.0 g of hydrogen sulphide, use to the formula: number of moles = Given massMolecular Mass\dfrac{{{\text{Given mass}}}}{{{\text{Molecular Mass}}}}. For doing the calculation of moles, you also need to calculate the molecular mass of hydrogen sulphide.

Complete step by step solution:
As you know, the chemical formula of hydrogen sulphide is H2S{H_2}S.
Thus, molecular mass of H2S{H_2}S= 2 \timesAtomic weight of hydrogen + Atomic weight of sulphur{\text{2 \times Atomic weight of hydrogen + Atomic weight of sulphur}}
Atomic weight of Hydrogen, H=1g/molH = 1 g/mol
Atomic weight of Sulphur, S=32g/molS = 32 g/mol
Therefore, molecular mass of H2S{H_2}S = 2×1+32=34 g/mol2 \times 1 + 32 = 34{\text{ }}g/mol
We are asked to calculate the number of moles contained in a sample of 35.0 g of hydrogen sulphide.
Thus, given mass of H2S{H_2}S =35.0g= 35.0 g
Now, formula to calculate number of moles = Given massMolecular Mass\dfrac{{{\text{Given mass}}}}{{{\text{Molecular Mass}}}}
Therefore, number of moles of H2S{H_2}S = 35.034=1.03 mol\dfrac{{35.0}}{{34}} = 1.03{\text{ }}mol
Hence, option A is the correct answer.
Additional information: Mole, having symbol mol, is the SI unit to measure the amount of substance. One mole of any substance contains Avogadro's number (NA{N_A}) of particles i.e., 6.022×1023particles6.022 \times {10^{23}}particles and mass of one mole of a substance in grams is equivalent to its molar mass. Thus, 34 g of hydrogen sulphide constitutes 1 mole.

So the answer to this question is option A.

Note: One should also have the information regarding the percentage of a particular element in a compound. For this, mass percent of the elements present in a compound is usually calculated.
Mass percent of the elements can be calculated as:
Mass % of an element = mass of that element in the compoundmolar mass of the compound×100\dfrac{{{\text{mass of that element in the compound}}}}{{{\text{molar mass of the compound}}}} \times 100
Let us calculate mass percent of the elements present in hydrogen sulphide (H2S{H_2}S):
Mass % of hydrogen, H in H2S{H_2}S = 2×134×100=5.88 %\dfrac{{2 \times 1}}{{34}} \times 100 = 5.88{\text{ }}\%
Mass % of sulphur, S in H2S{H_2}S = 3234×100=94.11 %\dfrac{{32}}{{34}} \times 100 = 94.11{\text{ }}\%