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2 years ago

19. Why should all measurements be done multiple times?

Chemistry

2 answers:

Alja [10]2 years ago

8 0

Answer:

Increasing precision with multiple measurements

Explanation:

The more measurements you take (provided there is no problem with the clock!), the better your estimate will be. Taking multiple measurements also allows you to better estimate the uncertainty in your measurements by checking how reproducible the measurements are.

Kryger [21]2 years ago

4 0

Answer:

All measurements should be done twice to absolutely make sure that you have the correct measurement and to avoid any mistakes if you are like building lets say a table or doing a equation. The saying is measure twice cut once

Explanation:

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How much 10.0 M HNO must be added to 1.00 L of a buffer that is 0.0100 M acetic acid and 0.100 M sodium acetate to reduce the pH

Naya [18.7K]

Explanation:

It is given that molarity of acetic acid = 0.0100 M

Therefore, moles of acetic acid = molarity of acetic acid × volume of buffer

Moles of acetic acid = 0.0100 M × 1.00 L

= 0.0100 mol

Similarly, moles of acetate = molarity of sodium acetat × volume of buffer

= 0.100 mol

When $HNO_{3}$ is added, it will convert acetate to acetic acid.

Hence, new moles acetic acid = (initial moles acetic acid) + (moles $HNO_{3}$ )

= 0.0100 mol + x

New moles of sodium acetate = (initial moles acetate) - (moles $HNO_{3}$ )

= 0.100 mol - x

According to Henderson - Hasselbalch equation,

pH = $pK_{a} + log\frac{[conjugate base]}{[weak acid]}$

pH = $pKa + log\frac{(new moles of sodium acetate)}{(new moles of acetic acid)}$

4.95 = 4.75 + $log\frac{(0.100 mol - x)}{(0.0100 mol + x)}$

$log\frac{(0.100 mol - x)}{(0.0100 mol + x)}$ = 4.95 - 4.75

= 0.20

$\frac{(0.100 mol - x)}{(0.0100 mol + x)}$ = antilog (0.20)

= 1.6

Hence, x = 0.032555 mol

Therefore, moles of $HNO_{3}$ = 0.032555 mol

volume of $HNO_{3}$ = $\frac{moles HNO_{3}}{molarity of HNO_{3}}$

= $\frac{0.032555 mol}{10.0 M}$

= 0.0032555 L

or, = 3.25 (as 1 L = 1000 mL)

Thus, we can conclude that volume of $HNO_{3}$ added is 3.26 mL.

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Answer:

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Explanation:

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