*Looking for simple explaination of how to solve these problems, NOT just a solu

Question

*Looking for simple explaination of how to solve these problems, NOT just a solution.  I am familiar with dimensional analysis, just having trouble remembering how to work out these problems with various units (grams, ml, percentages)  Thank you!  Points to the most helpful!

Given 4.0 mL of 2.0M NaOH, calculate the number of grams of NaOH in the solution.
(MW NaOH 39.99 g/mol) g
Given 4.5 mL of sulfuric acid (98%) calculate the number of mmols in the solution.
(MW H2SO4: 98.08 g/mol, density: 1.840 g/mL) mmol
Given 6.2 g of HBr calculate the volume (mL) of a 48% solution.
(MW HBr: 80.91 g/mol, density: 1.49 g/mL)

Explanation / Answer

1. You must go from mL to g

You have mL which can be converted to L,

mol/L

and g/mol

String them together and you get

0.004 L x (2.0mol/1L) x (39.99g/mol) = 0.31992g

2. You need to go from mL of solution to mmol of H2SO4

You have mL of solution,

mL H2SO4 per mL solution

g/mL

g/mol

and mmol is 0.001 mol

String these together

4.5 mL x (98 part H2SO4/100 part solution) x (1.840 g/mL) x (1mol/98.08g) x (1000mmol/1mol)

= 82.73 mmol

3. You go from g HBr to mL of solution.

You have g,

g/mL

g/mol

and percentage of HBr in desired solution.

In this question, g/mol is not necessary as it is not present in either of the end points, and also is not found in any other conversion factors.

String the remainder together.

6.2g x (1mL/1.49g) x (100 part solution / 48 part HBr) = 8.67g

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