The metal is sodium, Na.
<u>Explanation:</u>
K₂O is an ionic compound in which K is in the oxidation state of +1 and it belongs to group 1.
Group 1 elements also form oxides with the metals with the general formula M₂O and M being Na, K, Li and so on.
Metals Like sodium and Potassium are so brittle in nature and also their oxides.
So the other metal that form metal oxide which is brittle as well as ionic in nature, and so the metal oxide is Na₂O.
So the metal is sodium, Na.
The idea here is that you need to figure out how many moles of magnesium chloride,
MgCl
2
, you need to have in the target solution, then use this value to determine what volume of the stock solution would contain this many moles.
As you know, molarity is defined as the number of moles of solute, which in your case is magnesium chloride, divided by liters of solution.
c
=
n
V
So, how many moles of magnesium chloride must be present in the target solution?
c
=
n
V
⇒
n
=
c
⋅
V
n
=
0.158 M
⋅
250.0
⋅
10
−
3
L
=
0.0395 moles MgCl
2
Now determine what volume of the target solution would contain this many moles of magnesium chloride
c
=
n
V
⇒
V
=
n
c
V
=
0.0395
moles
3.15
moles
L
=
0.01254 L
Rounded to three sig figs and expressed in mililiters, the volume will be
V
=
12.5 mL
So, to prepare your target solution, use a
12.5-mL
sample of the stock solution and add enough water to make the volume of the total solution equal to
250.0 mL
.
This is equivalent to diluting the
12.5-mL
sample of the stock solution by a dilution factor of
20
.
Answer:
-177.9 kJ.
Explanation:
Use Hess's law. Ca(s) + CO2(g) + 1/2O2(g) → CaCO3(s) ΔH = -812.8 kJ 2Ca(s) + O2(g) → 2CaO(s) ΔH = -1269.8 kJ We need to get rid of the Ca and O2 in the equations, so we need to change the equations so that they're on both sides so they "cancel" out, similar to a system of equations. I changed the second equation. Ca(s) + CO2(g) + 1/2O2(g) → CaCO3(s) ΔH = -812.8 kJ 2CaO(s) → 2Ca(s) + O2(g) ΔH = +1269.8 kJ The sign changes in the second equation above since the reaction changed direction. Next, we need to multiply the first equation by two in order to get the coefficients of the Ca and O2 to match those in the second equation. We also multiply the enthalpy of the first equation by 2. 2Ca(s) + 2CO2(g) + O2(g) → 2CaCO3(s) ΔH = -1625.6 kJ 2CaO(s) → 2Ca(s) + O2(g) ΔH = +1269.8 kJ Now we add the two equations. The O2 and 2Ca "cancel" since they're on opposite sides of the arrow. Think of it more mathematically. We add the two enthalpies and get 2CaO(s) + 2CO2(g) → 2CaCO3(s) and ΔH = -355.8 kJ. Finally divide by two to get the given equation: CaO(s) + CO2(g) → CaCO3(s) and ΔH = -177.9 kJ.
Answer: The mass percentage of 
is 5.86%
Explanation:
To calculate the mass percentage of in the sample it is necessary to know the mass of the solute ( in this case), and the mass of the solution (pesticide sample, whose mass is explicit in the letter of the problem).
To calculate the mass of the solute, we must take the mass of the 
precipitate. We can establish a relation between the mass of and using the stoichiometry of the compounds:
Since for every mole of Tl in there are two moles of Tl in , we have:
Using the molar mass of we have:
Finally, we can use the mass percentage formula:
Answer:
Choose the least electronegative atom other than H.
Explanation:
A Lewis structure consists of <em>terminal atoms</em> and one or more <em>central atoms</em>.
H can be <em>only a terminal atom</em> because it can form only one bond.
So the central atom must be either C or O.
The central atom is the less electronegative atom: C.
So, start the Lewis structure with a central C atom.
Then attach an O atom to get C-O.
Finally, attach the H atoms.
The condensed formula often gives you a clue where they go.
The formula CH₃OH implies that there are 3 H atoms on C and one on O.
The connectivity of the atoms is then as in the diagram below.
