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3 years ago

Why is a control group important in an experiment?

Chemistry

1 answer:

bazaltina [42]3 years ago

8 0

A control group is an essential part of an
experiment because it allows you to eliminate and isolate these variables.

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Find the total number of atoms in a sample of cocaine hydrochloride, c17h22clno4, of mass 23.0 mg .

Nataliya [291]

From the periodic table:
mass of carbon = 12 grams
mass of hydrogen = 1 gram
mass of nitrogen = 14 grams
mass of oxygen = 16 grams
mass of chlorine = 35.5 grams
Therefore,
molar mass of <span>c17h22clno4 = 17(12) + 22(1) + 35.5 + 14 + 4(16) = 339.5 grams

number of moles = mass / molar mass
number of moles = (23*10^-3) / (339.5)
number of moles = 6.77 * 10^-5 moles

number of atoms = number of moles * Avogadro's number
number of atoms = 6.77*10^-5 * 6.022*10^-23
number of atoms = 4.079 * 10^-27 atoms</span>

3 0

4 years ago

A 200.0 mL solution of 0.40 M ammonium chloride was titrated with 0.80 M sodium hydroxide. What was the pH of the solution after

choli [55]

Answer:

9.25

Explanation:

Let first find the moles of $NH_4Cl$ and $NaOH$

number of moles of $NH_4Cl$ = 0.40 mol/L × 200 × 10⁻³L

= 0.08 mole

number of moles of $NaOH$ = 0.80 mol/L × 50 × 10⁻³L

= 0.04 mole

The equation for the reaction is expressed as:

$NH^+_{4(aq)} \ + OH^-_{(aq)} ------> NH_{3(g)} \ + H_2O_{(l)}$

The ICE Table is shown below as follows:

$NH^+_{4(aq)} \ + OH^-_{(aq)} ------> NH_{3(g)} \ + H_2O_{(l)}$

Initial (M) 0.08 0.04 0

Change (M) - 0.04 -0.04 + 0.04

Equilibrium (M) 0.04 0 0.04

$K_a*K_b = 10^{-14} \ at \ 25^0C$

$K_a = \frac{10^{-14}}{K_b}$

$K_a = \frac{10^{-14}}{1.76*10^{-5}}$

$K_a= 5.68*10^{10}$

$pK_a = - log \ (K_a)$

$pK_a = - log \ (5.68*10^{-10})$

$pK_a = 9.25$

$pH = pKa + \ log (\frac{HB}{HA} )$ for buffer solutions

$pH = pKa + \ log (\frac{moles \ of \ base }{ moles\ of \ acid} )$ since they are in the same solution

$pH = 9.25 + \ log (\frac{0.04 }{ 0.04} )$

$pH = 9.25$

8 0

3 years ago

What is the mole ratio to correct balance the reaction below? __KBr + __Ca3N2--> __CaBr2 + __K3N

jonny [76]

Explanation:

3CaBr2 + 2K3N → 6KBr + Ca3N2

7 0

3 years ago

The ion p3− has _____ protons and _____ electrons. enter your answers as integers separated by a comma.'

katrin2010 [14]

The symbol $P$ is for phosphorus having atomic number 15. That means it has $15 protons and 15 electrons$ in its neutral state.

The given symbol $P^{3-}$ has a -3 charge that means it has gained 3 electrons so, the number of electrons in the $P^{3-}$ is: $15+3 = 18$ . The number of protons will remain same that is the number of protons = 15.

So, the ion $P^{3-}$ has $15 protons and 18 electrons$ that gives $15-18=-3$ charge on the $P^{3-}$ ion.

So, the answer is $15 , 18$ .

7 0

3 years ago

What can you conclude from the fact that electrons orbit far away from atomic nuclei?

suter [353]

Electrons are extremely small. Atoms are comprised mostly of empty space. Protons have a positive charge.
Hope this helps.

5 0

3 years ago