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3 years ago

What experimental observations indicate a chemical change is taking place?

1 answer:

6 0

A chemical change is characterized of the formation of new substances or a chemical reaction. There are a number of observations that we can see if this type of change happens. One would be the formation of gas bubbles, this indicates that one of the products is a gas. Another observation would be a formation of a precipitate in the solution, it would indicate that the new solid formed is not soluble in the solution. A permanent color change in the solution would also indicate a chemical change because it may be that the new substance that is formed has its own distinct color when in solution.

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Solution A is a 1.00 L buffer solution that is 1.188 M in acetic acid and 1.188 M in sodium acetate. Acetic acid has a pKa of 4.

Tomtit [17]

Answer:

pH change is -0.07

Explanation:

Using H-H equation for acetic acid:

pH = pKa + log [Acetate salt] / [Acetic acid]

Replacing:

pH = 4.74 + log[1.188M] / [1.188M]

pH = 4.74

The HCl reacts with sodium acetate producing acetic acid, thus:

HCl + CH₃COONa → CH₃COOH + NaCl

That means the final moles of sodium acetate are initial moles - moles of HCl and moles of acetic acid are initial moles + moles of HCl.

As the volume of the buffer is 1.0L, initial moles of both substances are 1.188moles. After reaction, the moles are:

sodium acetate: 1.188mol - 0.1mol = 1.088mol

Acetic acid: 1.188mol + 0.1mol = 1.288mol

Using again H-H equation:

pH = 4.74 + log[1.088M] / [1.288M]

pH = 4.67

pH change is: 4.67 - 4.74 = -0.07

7 0

3 years ago

A compound is 7.74% hydrogen and 92.26% carbon by mass. At 100°C a 0.6883 g sample of the gas occupies 250 mL when the pressure

ycow [4]

Answer: The molecular formula for the compound is $C_6H_6$

Explanation:

We are given:

Percentage of C = 92.26 %

Percentage of H = 7.74 %

Let the mass of compound be 100 g. So, percentages given are taken as mass.

Mass of C = 92.26 g

Mass of H = 7.74 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of Carbon = $\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=\frac{92.26g}{12g/mole}=7.68moles$

Moles of Hydrogen = $\frac{\text{Given mass of Hydrogen}}{\text{Molar mass of Hydrogen}}=\frac{7.74g}{1g/mole}=7.74moles$

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 7.68 moles.

For Carbon = $\frac{7.68}{7.68}=1$

For Hydrogen = $\frac{7.74}{7.68}=1$

Step 3: Taking the mole ratio as their subscripts.

The ratio of C : H = 1 : 1

The empirical formula for the given compound is $CH$

Calculating the molar mass of the compound:

To calculate the molecular mass, we use the equation given by ideal gas equation:

PV = nRT

Or,

$PV=\frac{m}{M}RT$

where,

P = pressure of the gas = 820 torr

V = Volume of gas = 250 mL = 0.250 L (Conversion factor: 1 L = 1000 mL )

m = mass of gas = 0.6883 g

M = Molar mass of gas = ?

R = Gas constant = $62.3637\text{ L. torr }mol^{-1}K^{-1}$

T = temperature of the gas = $100^oC=(100+273)K=373K$

Putting values in above equation, we get:

$820torr\times 0.250L=\frac{0.6883g}{M}\times 62.3637\text{ L torr }mol^{-1}K^{-1}\times 373K\\\\M=\frac{0.6883\times 62.3637\times 373}{820\times 0.250}=78.10g/mol$

For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.

The equation used to calculate the valency is:

$n=\frac{\text{Molecular mass}}{\text{Empirical mass}}$

We are given:

Mass of molecular formula = 78.10 g/mol

Mass of empirical formula = 13 g/mol

Putting values in above equation, we get:

$n=\frac{78.10g/mol}{13g/mol}=6$

Multiplying this valency by the subscript of every element of empirical formula, we get:

$C_{(1\times 6)}H_{(1\times 6)}=C_6H_6$

Hence, the molecular formula for the compound is $C_6H_6$

8 0

3 years ago

Write the net ionic reaction for the following double replacement reaction:

Schach [20]

Net ionic equation

Cu²⁺(aq)+S²⁻(aq)⇒CuS(s)

<h3>Further explanation</h3>

Double-Replacement reactions. Happens if there is an ion exchange between two ion compounds in the reactant to form two new ion compounds in the product

In the ion equation, there is a spectator ion that is the ion which does not react because it is present before and after the reaction

When these ions are removed, the ionic equation is called the net ionic equation

For gases and solids including water (H₂O) can be written as an ionized molecule

Reaction

CuSO₄(aq)+Na₂S(aq)⇒CuS(s)+Na₂SO₄

ionic equation

Cu²⁺(aq)+SO₄²⁻(aq)+2Na⁺(aq)+S²⁻(aq)⇒CuS(s)+2Na⁺(aq+SO₄²⁻(aq)

spectator ions : 2Na⁺ and SO₄²⁻

Net ionic equation

Cu²⁺(aq)+S²⁻(aq)⇒CuS(s)

6 0

3 years ago

Help help help help help

luda_lava [24]

The sum is 34.688 m.

If m is a variable, then the m would be attached to 34.688.

7 0

3 years ago

Read 2 more answers

Which are chemical processes? (1 rusting of a nail, 2 freezing of water, 3 decomposition of water into hydrogen and oxygen gases

konstantin123 [22]

The answer is a hope it helps

4 0

3 years ago