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Travka [436]
3 years ago
6

Which of the following is evidence of a chemical change?

Chemistry
2 answers:
krek1111 [17]3 years ago
5 0
<span>the formation of a gas
</span>
larisa86 [58]3 years ago
5 0

Answer:

the formation of a gas

Explanation:

The chemical change is one in which some chemical reaction occur.

a) Phase change : it is simply change of one state of matter to another.

For example conversion of ice to liquid water, where there is no change in chemical composition of water and only the physical state is changing.

b) formation of gas: it is possible when some substance breaks into some other components or some substance reacts with other. This is definitely a chemical change as bonds will break and may be new bonds will form.

For example decomposition of calcium carbonate gives carbon dioxide (a gas) and calcium oxide.

c) mass change: it could be due to evaporation of water from a substance. Which must be a physical change.

d) surface area: change in surface is area must be due to change in state or physical modifications in state of a substance.

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8 0
3 years ago
A chemist dissolves 867. mg of pure barium hydroxide in enough water to make up 170. mL of solution. Calculate the pH of the sol
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Answer: The pH of the solution is 11.2

Explanation:

Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.

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

where,

n = moles of solute

V_s = volume of solution in ml

moles of Ba(OH)_2 = \frac{\text {given mass}}{\text {Molar mass}}=\frac{0.867g}{171g/mol}=0.00507mol         (1g=1000mg)

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

Molarity=\frac{0.00507\times 1000}{170}

Molarity=0.0298

pH or pOH is the measure of acidity or alkalinity of a solution.

pH is calculated by taking negative logarithm of hydrogen ion concentration.

pOH=-\log [OH^-]

Ba(OH)_2\rightarrow Ba^{2+}+2OH^{-}

According to stoichiometry,

1 mole of Ba(OH)_2 gives 2 mole of OH^-

Thus 0.0298 moles of Ba(OH)_2 gives =\frac{2}{1}\times 0.0298=0.0596 moles of OH^-

Putting in the values:

pOH=-\log[0.0596]=2.82

pH+pOH=14

pH=14-2.82

pH=11.2

Thus the pH of the solution is 11.2

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3 0
3 years ago
Determine the number of moles of water assicated with the salt.
Nookie1986 [14]

Answer:

Divide the mass of your anhydrous (heated) salt sample by the molar mass of the anhydrous compound to get the number of moles of compound present. In our example, 16 grams / 160 grams per mole = 0.1 moles. Divide the mass of water lost when you heated the salt by the molar mass of water, roughly 18 grams per mole.In order to determine the formula of the hydrate, [Anhydrous Solid⋅xH2O], the number of moles of water per mole of anhydrous solid (x) will be calculated by dividing the number of moles of water by the number of moles of the anhydrous solid (Equation 2.12. 6).

6 0
3 years ago
Glucose (C6H12O6) can be fermented to yield ethanol (CH3CH2OH) and carbon dioxide (CO2). C6H12O6⟶2CH3CH2OH+2CO2 The molar mass o
jekas [21]

Answer:

The % yield is 74.45 %

Explanation:

<u>Step 1:</u> The balanced equation

C6H12O6⟶2CH3CH2OH+2CO2

<u>Step 2</u>: Data given

Molar mass glucose = 180.15 g/mol

Molar mass of ethanol = 46.08 g/mol

Molar mass of carbon dioxide = 44.01 g/mol

Mass of glucose = 61.5 grams

Mass of ethanol = 23.4 grams

<u>Step 3:</u> Calculate moles of glucose

Moles glucose = Mass glucose  / Molar mass of glucose

Moles glucose = 61.5 grams / 180.15 g/mol

Moles glucose = 0.341 moles

<u>Step 4:</u> Calculate moles of ethanol

1 mole of glucose consumed, produces 2 moles of ethanol and 2 moles of CO2

0.341 moles of glucose, will produce 2*0.341 = 0.682 moles of ethanol

<u>Step 5:</u> Calculate mass of ethanol

Mass ethanol = moles ethanol * Molar mass ethanol

Mass ethanol = 0.682 moles * 46.08 g/mol

Mass ethanol = 31.43 grams = theoretical mass

<u>Step 6:</u> Calculate % yield

% yield = actual mass / theoretical mass

% yield = (23.4 grams / 31.43 grams) * 100%

% yield = 74.45 %

The % yield is 74.45 %

7 0
3 years ago
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