An atom of magnesium has an atomic number of 12 and a mass number of 24. how many protons plus neutrons are in the nucleus

Express the concentration of a 0.0390 M aqueous solution of fluoride, F − , in mass percentage and in parts per million (ppm). A

Vadim26 [7]

Answer:

Mass percentage → 0.074 %

[F⁻] = 741 ppm

Explanation:

Aqueous solution of flouride → [F⁻] = 0.0390 M

It means that in 1L of solution, we have 0.0390 moles of F⁻

We need the mass of solution and the mass of 0.0390 moles of F⁻

Mass of solution can be determined by density:

1g/mL = Mass of solution / 1000 mL

Note: 1L = 1000mL

Mass of solution: 1000 g

Moles of F⁻ → 0.0390 moles . 19g /1 mol = 0.741 g

Mass percentage → (Mass of solute / Mass of solution) . 100

(0.741 g / 1000 g) . 100 = 0.074 %

Ppm = mass of solute . 10⁶ / mass of solution (mg/kg)

0.741 g . 1000 mg/1g = 741 mg

1000 g . 1 kg/1000 g = 1kg

741 mg/1kg = 741 ppm

5 0

3 years ago

What is a firedamp? A. a blanket-like object used to extinguish fires B. the remnants of a fire after it has been extinguished C

diamong [38]

Answer: D. A buildup of mostly methane gas, which is pontentially explosive.

Explanation:

Firedamp refers to a gas mixture, largely methane, that appear in underground coal mines. It is explosive at concentrations between 5 and 10% in the air.

8 0

3 years ago

An electrode has a negative electrode potential. Which statement is correct regarding the potential energy of an electron at thi

elena-14-01-66 [18.8K]

Answer:

C. An electron at this electrode has a higher potential energy than it has at a standard hydrogen electrode.

Explanation:

The standard hydrogen electrode (SHE) is used to measure the electrode potential of substances. The standard hydrogen electrode is arbitrarily assigned an electrode potential of zero. Recall that electrode potentials are always measured as reduction potentials in electrochemical systems.

For an electrode that has a negative electrode potential, electrons at this electrode have a higher potential energy compared to electrons at the standard hydrogen electrode. Electrons flow from this electrode to the hydrogen electrode.

On the other hand, a positive electrode potential implies that an electron at this electrode has a lower potential energy than it has at a standard hydrogen electrode. Hence electrons will flow from the standard hydrogen electrode to this electrode.

5 0

3 years ago

Calcium has the symbol Ca and its ions have a charge of +2. Chlorine has the symbol Cl and its ions have a charge of -1. In the

hodyreva [135]

Answer:

There are two chloride ions for each calcium ion

Explanation:

The compound has to have an overall neutral charge. Meaning that the positive charges from calcium have to be canceled out by the negative charges of chlorine.

If there are two chloride ions for each calcium ion, the charges would cancel themselves out (2 * -1 would cancel out with +2).

5 0

3 years ago

In a laboratory demonstration, a balloon filled with methane and oxygen was exposed to a flame. The result was a brief, large fl

Savatey [412]

Answer:

The equation is not correct:

[CH4 + O2 → CO2 + 2H2O]

Explanation:

The chemical formulas for methane, oxygen, and carbon dioxide are correct, but the equation is not balanced, so we really don't know idf the overall reaction is written correctly.

Let's balance the reaction:

CH4 + O2 → CO2

We need to have the same numbers of atoms on both sides.

Count the numbers of each atom:

Element Reactants Products Difference

C 1 1 0 Balanced

H 4 0 -4 XXX!!!!

O 2 2 0 Balanced

The hydrogens aren't showing up in the products. In fact, there is a product missing entirely from the reaction, H2O, water. The basic reaction is:

CH4 + O2 → CO2 + H2O

Now balance this reaction:

Element Reactants Products Difference

C 1 1 0 Balanced

H 4 2 -2 Hmmmm . . .

O 2 3 1 Uh = oh . . .

This reaction is not possible - there are either too many or too few element atoms (the "Difference").

We can adjust the coefficients for each of the molecules to balanced the equation. This is a bit tricky, but it consists of trying some coefficients that would make things balance. Only whole number coefficients are allowed in the final answer, although fractions might be used in the process to help find the whole numbers.

We need 2 H2O molecules to account for the 4 hydrogens on a single methane molecule

Step 1: CH4 + O2 → CO2 + 2H2O

That leads to:

Element Reactants Products Difference

C 1 1 0 Balanced

H 4 4 0 Balanced

O 2 4 2 Darn

We need more oxygen atoms, so:

Step 2: CH4 + 2O2 → CO2 + 2H2O

This leads to:

Element Reactants Products Difference

C 1 1 0 Balanced

H 4 4 0 Balanced

O 4 4 0 Balanced

This is a balanced reaction, and the correct chemical equation.

3 0

3 years ago