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3 years ago

28. After 3 substances are mixed, an odor emits

Chemistry

2 answers:

Lyrx [107]3 years ago

7 0

Answer:

a. chemical change

Explanation:

A chemical change can cause an odor, however a physical change cannot, and the use of thermal energy will only make an object colder, not give it an odor.

slavikrds [6]3 years ago

3 0

I'm pretty sure that the answer is a chemical change

a physical change is only something you can see and in the chemical change it is possible to smell it.

your welcome :)

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What is dissociation constant?

iragen [17]

In Chemistry, the dissociation constant describes a dissociation reaction in which a compound is broken up. It measures how likely the reaction will occur. For example for reaction AB -> A + B, the dissociation constant is equal to concentration of A x concentration of B / concentration of AB at equilibrium.

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4 years ago

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Which statement is true about energy changes?

Sindrei [870]

Answer:

Explanation:

energy can not be created or destroyed it can only be transferred or changed to one form to another.

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4 years ago

A 4.36-g sample of an unknown alkali metal hydroxide is dissolved in 100.0 mL of water. An acid-base indicator is added and the

Levart [38]

Answer:

a. 102.6g/mol

b. Rb⁺

Explanation:

a. The unknown base, XOH, <em>Where X is the alkali metal</em>, reacts with HCl thus:

XOH + HCl → H₂O + XCl

<em>Where 1 mole of the hydroxide reacts per mole of acid. </em>

Moles of HCl spent to reach the equivalence point are:

17.0mL = 0.017L ₓ (2.50mol / L) = 0.0425moles of HCl

As 1 mole of HCl reacts with 1 mole of base, moles of base are 0.0425 moles.

Molar mass of a compound is the ratio between mass in grams and moles of substance, that is:

4.36g / 0.0425mol =

b) Molar mass of OH is 17g/mol, thus, the molar mass of the alkali metal is:

102.6g/mol - 17g/mol = 85.6g/mol

The mass of Rb is 85.5g/mol, thus, the identity of the alkali metal is

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3 years ago

What is the pH of a mixture of equal volumes of 0.6 mM Lactic acid and 0.4 mM NaOH?

tino4ka555 [31]

Answer:

The pH of the mixture is approximately 4.2.

There's no equilibrium calculation involved if HCl is used instead of lactic acid. The pH of that solution will be approximately 3.7.

Explanation:

<h3>Lactic Acid</h3>

Lactic acid is a monoprotic acid. In other words, each lactic acid molecule can be ionized to release only one proton. Therefore, lactic acid will react with NaOH at a 1-to-1 ratio. The result will be one unit of the anion of lactate ion.

Lactic acid is in excess. All NaOH will be consumed. Before any dissociation takes place, the solution will contain 0.2 mM of lactic acid and 0.4 mM of lactate ions.

Lactic acid is a weak acid. The following equilibrium will take place in the solution:

$\rm C_3H_6O_3 \leftrightharpoons {C_3H_5O_3}^{-} + H^{+}$ .

Let the increase in the concentration of protons in the solution be $x\rm \;M$ . Construct a RICE table:

$\begin{array}{c|ccccc}\rm \textbf{R}&\rm C_3H_6O_3 & \leftrightharpoons &\rm {C_3H_5O_3}^{-}& +& \rm H^{+}\\\textbf{I} & 0.2\times 10^{-3} && 0.4\times 10^{-3} \\\textbf{C} & -x & & +x & & +x\\\textbf{E} & 0.2\times 10^{-3} -x & & 0.4\times 10^{-3} + x & & x\end{array}$ .

The pKa value of lactic acid is 3.86. Therefore, $K_{\rm a} = 10^{-3.86}$ . By the definition of the acid dissociation constant $K_{\rm a}$ ,

$\begin{aligned} K_{\rm a} &= \frac{\rm [H^{+}][{C_3H_5O_3}^{-}]}{[\rm C_3H_6O_3]}\\& = \frac{x(0.4\times 10^{-3} +x)}{(0.6 \times 10^{-3} - x)}\end{aligned}$ .

Given that $K_{\rm a} = 10^{-3.86}$ , solve for $x$ :

$\displaystyle \frac{x(0.4\times 10^{-3} - x)}{0.2 \times 10^{-3}-x} = 10^{-3.86}$ .

There might be more than one solutions. However, the correct solution shall ensure that all concentrations are greater than zero. In this case,

$x \approx 5.7\times 10^{-5}$ .

By the definition of pH,

$\rm pH = -\log_{10}{[H^{+}]} = -\log_{10}{5.7\times 10^{-5}} \approx 4.2$ .

The Henderson-Hasselbalch equation will yield a similar result.

Similar to lactic acid, HCl is also monoprotic. The solution will contain 0.2 mM of HCl and 0.4 mM of NaCl before any ionization takes place.

Unlike lactic acid, all that 0.2 mM of HCl will ionize to produce protons and chloride ions. The final proton concentration in the solution will be 0.2 mM. As a result,

$\rm pH = - \log_{10}{[H^{+}]} = -\log_{10}{0.2\times 10^{-3}} \approx 3.6$ .

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4 years ago

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jekas [21]

Ksp = [Cu^+]^2 [CO3^2-]

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4 years ago

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