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3 years ago

10

For the following measurements , 27.5 x 0.125 x 13= 44.6875 , choose the answer that is rounded to the correct number of signifi

cant figures.
A-40
B-45
C-44.7
D-44.69

1 answer:

sergejj [24]3 years ago

4 0

The Answer is C-44.7

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3 years ago

How many cobalt atoms are in 345 g of cobalt

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Answer:

$\boxed {\boxed {\sf About \ 3.53 \ *10^{24}atoms \ Co}}$

Explanation:

To convert from grams to atoms:

Convert grams to moles
Convert moles to grams

1. <u>Convert grams to moles</u>

First, find the molar mass of cobalt using the Periodic Table of Elements.

Cobalt (Co): 58.93319 g/mol

Next, use this mass as a ratio or fraction.

$\frac{58.93319 \ g\ Co}{1 \ mol \ Co}$

Multiply the mass of the given sample (345 grams) by this ratio.

$345 \ g \ Co *\frac{58.93319 \ g\ Co}{1 \ mol \ Co}$

Flip the fraction so the grams of Cobalt will cancel each other out when multiplying.

$345 \ g \ Co *\frac{1 \ mol \ Co}{58.93319 \ g\ Co}$

$345 \ *\frac{1 \ mol \ Co}{58.93319 }$

$\frac{345 \ mol \ Co}{58.93319 } =5.854086636 \ mol \ Co$

2. <u>Convert moles to atoms</u>

Use Avogadro's Number, which tells us the number of units (in this case atoms) in 1 mole.

$6.022 *10^{23} \ atoms/mol$

Use this number as a ratio or fraction.

$\frac{6.022 * 10^{23} \ atoms \ Co}{1 \ mol \ Co}}$

Multiply this ratio by the number of moles we found.

$5.854086636 \ mol \ Co*\frac{6.022 * 10^{23 }\ atoms \ Co}{1 \ mol \ Co}}$

The moles of Cobalt will cancel.

$5.854086636 \ *\frac{6.022 * 10^{23 }\ atoms \ Co}{1 }}$

$5.854086636 \ *{6.022 * 10^{23 }\ atoms \ Co}$

$3.52533097*10^{24} \ atoms \ Co$

3.<u>Round</u>

The original measurement of 345 has 3 significant figures (3, 4, and 5). We must round to 3 sig figs, which is the hundredth place for this measurement.

$3.52533097*10^{24} \ atoms \ Co$

The 5 in the thousandth place tells us to round the 2 to a 3.

$3.53 \ *10^{24}atoms \ Co$

There are about <u>3.53*10²⁴ atoms of cobalt in 345 grams.</u>

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3 years ago