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Phantasy [73]
3 years ago
6

Which set of procedures and observations indicates a chemical change?

Chemistry
1 answer:
Flauer [41]3 years ago
4 0
The answer is (4), (3) is merely a change in composition, thus not chemical but physical.

Answer: (4).
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Dolomite is a mixed carbonate of calcium and magnesium. Calcium and magnesium carbonates both decompose upon heating to produce
Setler79 [48]

Answer:

72.03 %

Explanation:

Total mass of dolomite = 9.66 g

Let the mass of Magnesium carbonate = x g

The mass of calcium carbonate = 9.66 - x g

Calculation of the moles of Magnesium carbonate as:-

Molar mass of Magnesium carbonate = 122.44 g/mol

The formula for the calculation of moles is shown below:

moles = \frac{Mass\ taken}{Molar\ mass}

Thus,

Moles= \frac{x\ g}{84.3139\ g/mol}=\frac{x}{84.3139}\ mol

Calculation of the moles of calcium carbonate as:-

Molar mass of calcium carbonate = 100.0869 g/mol

Thus,

Moles= \frac{9.66 - x\ g}{100.0869\ g/mol}=\frac{9.66 - x}{100.0869}\ mol

According to the reaction shown below:-

MgCO_3\rightarrow MgO+CO_2

CaCO_3\rightarrow CaO+CO_2

In both the cases, the oxides formed from the carbonates in the 1:1 ratio.

So, Moles of MgO = \frac{x}{84.3139}\ mol

Molar mass of MgO = 40.3044 g/mol

Thus, Mass = Moles*Molar mass = \frac{x}{84.3139}\times 40.3044 \ g

Moles of CaO = \frac{9.66 - x}{100.0869}\ mol

Molar mass of CaO = 56.0774 g/mol

Thus, Mass = Moles*Molar mass = \frac{9.66 - x}{100.0869}\times 56.0774 \ g

Given that total mass of the oxide = 4.84 g

Thus,

\frac{x}{84.3139}\times 40.3044 +\frac{9.66 - x}{100.0869}\times 56.0774=4.84

\frac{40.3044x}{84.3139}+56.0774\times \frac{-x+9.66}{100.0869}=4.84

-694.1618435x+45673.48749\dots =40843.38968\dots

x=\frac{4830.09780\dots }{694.1618435}

x=6.9582

Thus, the mass of Magnesium carbonate = 6.9582 g

\%\ mass=\frac{Mass_{MgCO_3}}{Total\ mass}\times 100

\%\ mass=\frac{6.9582}{9.66}\times 100=72.03\ \%

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