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4 years ago

Calculate the number of moles of caco3 (calcium carbonate, or limestone) in a 20.0g sample of this substance

1 answer:

6 0

First calculate for the molar mass of the given formula unit, CaCO₃. This can be done by adding up the product when the number of atom is multiplied to its individual molar mass as shown below.

molar mass of CaCO₃ = (1 mol Ca)(40 g Ca/mol Ca) + (1 mol C)(12 g of C/1 mol of C) + (3 mols of O)(16 g O/1 mol O) = 100 g/mol of CaCO₃

Then, divide the given amount of substance by the calculated molar mass.
number of moles = (20 g)(1 mol of CaCO₃/100 g)
number of moles = 0.2 moles of CaCO₃

<em>Answer: 0.2 moles</em>

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The density of concentrated ammonia, which is 28.0% w/w nh3, is 0.899 g/ml. what volume of this reagent should be diluted to 1.0

vlada-n [284]

Answer: 2.4 ml

Solution :

Molar mass of $NH_3$ = 17 g/mole

Given,: 28% w/w of $NH_3$ solution means 28 g of ammonia in 100 g of solution.

Mass of solution = 100 g

Now we have to calculate the volume of solution.

$Volume=\frac{Mass}{Density}=\frac{100g}{0.899g/ml}=111.2ml$

Molarity : It is defined as the number of moles of solute present in one liter of solution.

$Molarity=\frac{n\times 1000}{V_s}$

where,

n = moles of solute $NH_3=\frac{\text {given mass}}{\text {molar mass}}=\frac{28}{17}=1.65moles$

$V_s$ = volume of solution in liter = 0.11 L

Now put all the given values in the formula of molarity, we get

$Molarity=\frac{1.65moles}{0.11L}=15mole/L$

Using molarity equation:

$M_1V_1=M_2V_2$

$15\times V_1=0.036\times 1.0\times 10^{3}$

$V_1=2.4ml$

6 0

3 years ago

A sample of gas occupies a volume of 4.5 L at 20 Celsius. What volume will it occupy at -15 celsius, if the pressure remains con

nataly862011 [7]

Answer: 3.96L

Explanation:

PV = nRT

The way I like to do it, it's I get rid of whatever I do not need.

We have to do an equation for sure to make both sides equal and find our desired result.

The pressure is constant, so it would be constant in both sides, therefore, there is no point in using it.

The R is a constant used in both sides so there is no point on using it either.

We don't need to work with moles in this case, so let's forget about the moles.

Therefore we are left with only V (volume ) and T(Temperature)

Which would logically make this:

V1/T1 = V2/T2

T1/V1 = T2/V2

Both of these would work, we always use whatever makes our calculations easier without complicating our lives with the algebra.

That should remind you of Charles' Law

Transform degrees into kelvins

20 + 273.15 = 293.15K

-15 + 273.15 = 258.15K

So, 4.5L/293.15K = V2/258.15K

V2 = (4.5L/293.15K) x 258.15K

V2 = 3.96L

8 0

3 years ago

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