Question

In a test tube, there is 18g of glucose (${{C}_{6}}{{H}_{12}}{{O}_{6}}$). 0.08 mole of glucose is taken out. Glucose left in the tube is:
A. 0.10g
B. 0.02g
C. 0.10 mole
D. 3.60g

Answer 1

Try to find out the molar mass of glucose and accordingly, find the total number of moles which are present. Now, the moles taken out need to be subtracted and with the remaining moles in the tube, the weight is needed to be taken out.

Complete step by step solution:
-In order to answer our question, we need to have a clear idea about the moles and molar mass of a substance. But before that, let us know what actually a mole is. 1 mole is the unit which tells us what particular mass of the element will have the Avogadro number of molecules in it. The Avogadro number is $6.022\times {{10}^{23}}$. For example, carbon has the molar mass of 12g. Then it means that 12g of carbon contains $6.022\times {{10}^{23}}$ atoms. The molar mass is different for all the elements and compounds and that helps us to distinguish between all of them. Suppose for a given element or compound, it’s molar mass, as well as the general weighing mass is given. So, there is a simple formula to calculate the number of moles of the element or compound which is:
$no.\,of\,mole=\dfrac{given\,mass}{molar\,mass}$
-However, in order to calculate the molar mass of a compound, the individual molar masses of the constituent atoms need to be known. For example, in the compound, ${{H}_{2}}O$, Hydrogen has a molar mass of 1 and oxygen has 16. But as there are 2 hydrogens present so total molar mass is $2\times 1+16=18g$.
-Now, let us calculate the molar mass of glucose. Molar masses of carbon, hydrogen and oxygen are 12g, 1g and 16g respectively. So:
$molar\,mas{{s}_{{{C}_{6}}{{H}_{12}}{{O}_{6}}}}=(12\times 6)+(12\times 1)+(16\times 6)=180g\,mo{{l}^{-1}}$
-Also, we have been given the given weight of glucose that is 18 grams. So, Using the formula, we can find out the moles of glucose that are inside the test tube. Which comes out to be:
$no\,of\,mole=\dfrac{18g}{180g\,mo{{l}^{-1}}}=0.1mole$
-Now, 0,08 moles are taken out, so the number of moles left in the test tube is $0.1-0.08=0.02\,mole$. Now, the weight of glucose can be found out by:
$weight=moles\times molar\,mass$
$weigh{{t}_{{{C}_{6}}{{H}_{12}}{{O}_{6}}}}=0.02\times 120=3.6g$

So, 3.6 grams of glucose are left in the test tube. So our final answer is option D.

NOTE: The number of moles is a dimensionless quantity. It is also to be noted that the unit of molar mass is not grams. Molar mass is represented in $g\,mo{{l}^{-1}}\,\,or\,\,g/mol$, unless it is given that 1 mole of substance is given.