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3 years ago

A toothpaste contains sodium fluoride (NaF) What percentage of Fluoride is present.(4cs)

Chemistry

1 answer:

MariettaO [177]3 years ago

7 0

Answer:

45.2%

Explanation:

To calculate the percent of an element in a compound we divide the molar mass of the element by the compound and multiply that by 100

First lets find the molar mass of Fluoride

Looking at the periodic table Fluoride has a molecular mass of 18.998 g

Now we need to find the molecular mass of NaF

Looking at a periodic table, Sodium (Na) has a molecular mass of 22.990g and Fluoride has a molecular mass of 18.998 so NaF has a molecular mass of 22.990(1) + 18.998(1) = 41.988g

Now we divide the mass of fluoride by the mass of sodium fluoride and multiply that by 100 to find the percentage of fluoride that is present in NaF

Mass of Fluoride = 18.998g

Mass of Sodium Fluoride = 41.988g

Percentage of fluoride present in NaF = (18.998g / 41.988g) * 100 = 45.2%

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In the PhET simulation window, click the radio button labeled Mystery in the Blocks menu on the right-hand side of the screen. U

Yuliya22 [10]

Answer:

B, D, E, C, A

Explanation:

We have 5 blocks with their respective masses and volumes.

Block Mass Volume

A 65.14 kg 103.38 L

B 0.64 kg 100.64 L

C 4.08 kg 104.08 L

D 3.10 kg 103.10 L

E 3.53 kg 101.00 L

The density (ρ) is an intensive property resulting from dividing the mass (m) by the volume (V), that is, ρ = m / V

ρA = 65.14 kg / 103.38 L = 0.6301 kg/L

ρB = 0.64 kg / 100.64 L = 0.0064 kg/L

ρC = 4.08 kg / 104.08 L = 0.0392 kg/L

ρD = 3.10 kg / 103.10 L = 0.0301 kg/L

ρE = 3.53 kg / 101.00 L = 0.0350 kg/L

The order from least dense to most dense is B, D, E, C, A

4 0

3 years ago

Which is the most accurate description of compounds?

baherus [9]

Answer: c.They have a unique set of properties that can be used as identifiers.

Explanation:

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.

Compounds can be decomposed into simpler constituents using chemical reactions.

Example: Water $(H_2O)$

$2H_2O\rightarrow 2H_2+O_2$

Compounds have different properties than the elements it is made up of.

Thus the most accurate description of compounds is that they have a unique set of properties that can be used as identifiers.

3 0

3 years ago

Isoelectric point. The isoelectric point (pI) is the pH at which a molecule has no net charge. The amino acid glycine has two io

timama [110]

Answer:

pI = 6.16

Explanation:

The pI is given by the average of the pKas that are involved. In this case,

Pka of carboxylic acid was given as 2.72 and that of the Amino group was given as 9.60. the average would then be ½(2.72+9.60)

= 6.16

6 0

3 years ago

If 12.5 grams of strontium hydroxide is reacted with 150 mL of 3.5 M carbonic acid, identify the limiting reactant.

kiruha [24]

Answer:

Sr(OH)₂ will be the limiting reagent.

Explanation:

First of all, you should know the following balanced chemical equation:

2 H₂CO₃ + 2 Sr(OH)₂ → 4 H₂O + Sr₂(CO₃)₂

The balanced equation is based on the Law of Conservation of Mass, which says that matter cannot be created or destroyed. Therefore, the number of each type of atom on each side of a chemical equation must be the same.

The limiting reagent is one that is consumed first in its entirety, determining the amount of product in the reaction. When the limiting reagent is finished, the chemical reaction will stop.

To determine the limiting reagent, it is possible to use the reaction stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction). By stoichiometry the following amounts in moles react:

strontium hydroxide: 2 moles
carbonic acid: 2 moles

Now, you know the following masses of the elements:

Sr: 87.62 g/mole
O: 16 g/mole
H: 1 g/mole

So the molar mass of strontium hydroxide is:

Sr(OH)₂= 87.62 g/mole + 2*(16 g/mole + 1 g/mole)= 121.62 g/mole

You apply the following rule of three, if 121.62 grams of hydroxide are present in 1 mole, 12.5 grams in how many moles are they?

$moles of strontium hydroxide=\frac{12.5 grams*1 mole}{121.62 grams}$

moles of hydroxide= 0.103 moles

On the other hand, you have 150 ml of 3.5 M carbonic acid. Since molarity is the concentration of a solution expressed in the number of moles dissolved per liter of solution, you can apply the following rule of three: if in 1 L there are 3.5 moles of carbonic acid, in 0.150 L (being 1 L = 1000 mL, 0.150 L = 150 mL) how many moles of acid are there?

$molesofcarbonicacid=\frac{0.150 L*3.5 moles}{1 L}$

moles of carbonic acid= 0.525 moles

Finally, to calculate the limiting reagent, you can use a simple rule of three as follows: if by stoichiometry 2 mole of strontium hydroxide reacts with , how much moles of carbonic acid will be needed if 0.103 moles of strontium hydroxide react?

$molesofcarbonicacid=\frac{0.103 moles of strontium hydroxide*2 moles of carbonic acid}{2 moles of strontium hydroxide}$

moles of carbonic acid= 0.103 moles

But 0.525 moles are available. Since more moles are available than you need to react with 0.103 moles of strontium hydroxide, <u><em>Sr(OH)₂ will be the limiting reagent.</em></u>

7 0

3 years ago

Calculate the pH of a solution that is 0.210 M in nitrous acid (HNO2) and 0.290 M in potassium nitrite (KNO2). The acid dissocia

jeka94

Answer:

pH = 3.49

Explanation:

We have a buffer system formed by a weak acid (HNO₂) and its conjugate base (NO₂⁻ coming from KNO₂). We can calculate the pH of a buffer ssytem using the Henderson-Hasselbach equation.

pH = pKa + log [base] / [acid]

pH = -log Ka + log [NO₂⁻] / [HNO₂]

pH = -log 4.50 × 10⁻⁴ + log 0.290 M / 0.210 M

pH = 3.49

6 0

3 years ago