Of the animals in the bottom row, which one is most likely to be a keystone species?

4. Consider a 33.0 mL solution containing 0.0758 M NaF and 0.0955 M HF. What is the total number of moles of HF after the additi

Ostrovityanka [42]

Buffer solution resist the change in pH upon addition of small amount of strong acid or strong base.
Buffer consists of weak acid as HF / and its conjugate base NaF
When strong acid as HCl is added to buffer, it respond with its conjugate base to convert the strong acid to weak acid like this:
HCl (S.A) + NaF → NaCl + HF (W.A)
moles of HF we already have = M * V(in liters)
= 0.0955 M * 0.033 L = 3.15 x 10⁻³ mole
moles of HCl added = 8.00 x 10⁻⁵ mole
one mole HCl reacts with 1 mole NaF to give 1 mole HF
so the amount added to HF = 8.00 x 10⁻⁵
Total moles of HF present = (3.15 x 10⁻³) + (8.00 x 10⁻⁵) = 3.23 x 10⁻³ mole

4 0

3 years ago

A 46.9 gram sample of a substance has a volume of about 3.5 centimeters3. It is solid at a room temperature of 23ºC. Out of the

Masteriza [31]

Answer:- C. Hafnium.

Solution:- Mass of the sample is 46.0 g and it's volume is $3.5cm^3$ .

From mass and volume, we can calculate it's density using the formula:

$density=\frac{mass}{volume}$

$density=\frac{46.9g}{3.5cm^3}$

$density=\frac{13.4g}{cm^3}$

On the basis of the density, this substance could either be mercury or hafnium. Since the substance is a solid at room temperature where as mercury is liquid. So, it can't be mercury.

The right choice is C) Hafnium.

3 0

3 years ago

Explain why organic reactions occur at a slower rate than inorganic reactions. What do chemists use to speed these reactions up?

8_murik_8 [283]

The organic particles are molecules. Because of strong covalent bonding in the molecule, organic compounds do not react quickly. Reactions with organic compounds are generally slower than inorganic reactions due to this fact.

Increasing temperature speeds up a reaction because of there being more collisions and those collisions have higher energy. Also the high concentration of the chemicals, particle size and there being a suitable catalyst present. ( Though this process is harmful should it be used in modifying results in food grains and meats.)

5 0

3 years ago

Solid sodium hydrogen carbonate, NaHCO3, decomposes on heating according to the equation:

tekilochka [14]

Answer:

See explanation

Explanation:

First, let's write the balanced equation again:

2 NaHCO3(s) <-> Na2CO3(s) + H2O(g) + CO2(g)

Now, we know that the total pressure was 7.76 atm. This total pressure, is the sum of the pressure of water and CO2 like this:

Ptotal = Pwat + PCO2 (1)

This is the dalton's law for partial pressures.

The pressure can be also be relationed with the moles

Ratio of mole = Ratio of pressure

so, taking this in consideration we can say the following:

Pwater/PCO2 = moles water / moles CO2

As the only components exerting pressure are CO2 and Water (Because they are in gas phase), the total pressure can be splitted between the two of them so:

Pwater = Ptotal/2

Pwater = 7.76 / 2 = 3.88 atm

With this pressure, and using the ideal gas equation, we can know the moles of water:

PV = nRT

n = PV/RT using R = 0.082 L atm / K mol

n = 3.88 * 5 / 0.082 * (160+273)

n = 0.546 moles of water

b) now that we have the moles of water, we can actually know the moles that reacted originally from the sodium carbonate by stechiometry.

2NaHCO3(s) <-> Na2CO3(s) + H2O(g) + CO2(g) MMCO2 = 84 g/mol

the moles of NaHCO3 initially:

n = 100 / 84

n = 1.19 moles

so, If 1.19 moles of NaHCO3 reacted, and only produces 0.546 moles of water and CO2, then, the remaining moles of NaHCO3 is:

remaining moles = 1.19 - 0.546 = 0.644 moles

therefore the mass remaining:

mCO2 = 0.644 * 84

mCO2 = 54.096 g

c) As it was stated before, only the gaseous components are involved in the pressure, thus, in the kp expression which is:

Kp = Pwater * PCO2

Kp = 3.88 * 3.88

Kp = 15.0544

d) As the total pressure is 7.76 atm and the fact that NaHCO3 is solid, this component is not exerting any pressure in the reaction, as seen in the Kp expression, so it won't matter that if we raise a little the quantity of the reactant, it still has some remaining.

3 0

3 years ago

Which of the following is not true for atoms?

mariarad [96]

They are able to be divided by a chemical reaction

8 0

3 years ago