Fill in the blanks

What is the percent by mass of nahco3 in a solution containing 10 g of nahco3 dissolved in 400 ml of h2o?

Marat540 [252]

Answer is: the percent by mass of NaHCO₃ is 2,43%.
m(NaHCO₃) = 10 g.
V(H₂O) = 400 ml.
d(H₂O) = 1 g/ml.
m(H₂O) = V(H₂O) · d(H₂O).
m(H₂O) = 400 ml · 1 g/ml.
m(H₂O) = 400 g.
m(solution) = m(H₂O) + m(NaHCO₃).
m(solution) = 400 g + 10 g.
m(solution) = 410 g.
ω(NaHCO₃) = 10 g ÷ 410 g · 100%.
ω(NaHCO₃) = 2,43 %

7 0

3 years ago

Why does magnesium oxide have a high melting point?

Mandarinka [93]

Magnesium oxide is an ionic compound ( because it consists of a metal and a non-metal)

In ionic compounds, electrons from the outer shell exchange between the atoms so that they each get a full outer shell. Once these electrons are exchange, the atoms will become ions. One ion will have a positive charge, and the other ion will have a negative charge. The positive and negative ions then bond strongly together in a lattice structure, due to the electrostatic forces of attraction.

These electrostatic forces of attraction are very strong and require a lot of energy to break, as such the compound will have a high melting point.

__________________________________________

Now lets look at the ionic bonding between magnesium and oxygen:

In the outer shell of Magnesium, there are 2 electrons.

In the outer shell Oxygen, there are 6 electrons.

Magnesium gives it's two electrons to Oxygen, so that the Oxygen now has a full outer shell of 8 electrons. However, since Oxygen gained two electrons, it will form a negatively charged ion with a charge of -2.

Since Magnesium lost the two electrons, it's second shell (which has 8 eletrons) now becomes the outer shell. So Magnesium also now has a full outer shell. But since it has lost two electrons, it becomes a positively charged ion with a charge of + 2.

The positive Magnesium ion and negative Oxygen ion and now strongly attracted to each other, and form a strong ionic compound (magnesium oxide) with a lattice structure.

The electrostatic forces of attraction between the positive Magnesium and negative Oxygen are so strong that a lot of heat and energy are needed to break them.

Therefore magnesium oxide has a high melting point.

5 0

3 years ago

How much heat is lost when 575 grams molten iron at 1825 k becomes solid iron at 293 k? The melting point or iron is 1811 k.

Galina-37 [17]

Answer:

146 kJ

Explanation:

There are two heat flows in this question.

Heat lost on cooling + heat lost on solidifying = 0

q₁ + q₂ = 0

mCΔT + nΔHsol = 0

Data:

m = 575 g

C = 0.449 J·K⁻¹g⁻¹

T_i = 1825 K

T_f = 1811 K

ΔHsol = -13.8 kJ·mol⁻¹

Calculations:

(a) Heat lost on cooling

ΔT = T_f - T_i = 1811 K - 1825 K = -14 K

q₁ = mCΔT = 575 g × 0.449 J·K⁻¹g⁻¹ × (-14 K) = -361 J = -3.61 kJ

(b) Heat lost on solidifying

$n = \text{575 g} \times \dfrac{\text{1 mol}}{\text{55.84 g}} = \text{10.30 mol}\\\\q_{2} = n\Delta_{\text{sol}}H = \text{10.30 mol} \times \dfrac{\text{-13.8 kJ}}{\text{1 mol}}= \text{-142.1 kJ}$

(c) Total heat lost

q = q₁ + q₂ = -3.61 kJ - 142.1 kJ = -146 kJ

The heat lost was 146 kJ.

5 0

3 years ago

Determine the number of moles of air present in 1.35 L at 760 torr and 17.0 C. Which equation should you use?

Vanyuwa [196]

C. N = PV/RT is the anwser to your question

4 0

3 years ago

Read 2 more answers

Which of the following is not true for an exothermic reaction?

Gennadij [26K]

Answer:

The false statement regarding an exothermic reaction is: A. the products have a higher enthalpy than reactants

Explanation:

An exothermic reaction is a type of chemical reaction that involves the release of energy from the system to the surroundings. Thus increasing the temperature of the surroundings.

In this reaction, the enthalpy or energy of the reactants is greater than the enthalpy or energy of the products. ( $\Delta H_{f} (Products) < \Delta H_{f} (reactants)$ )

As the enthalpy change of a reaction: $\Delta H_{r} = \sum \Delta H_{f} (Products) - \sum \Delta H_{f} (reactants)$

Therefore, the enthalpy change for an exothermic reaction is negative ( $\Delta H_{r} < 0$ )

4 0

3 years ago