Smoke is a homo or hetero

What is a problem that would likely occur if two cultures had different calenderars

aksik [14]

The Sun, Moon, and stars have helped people for thousands of years. When you look into the sky, you will notice that they follow certain patterns. This happens most of the time, but not all of the time. Since most patterns repeat over and over, they have helped us keep track of time. These patterns have also helped us make calendars. Making calendars was a difficult task. Our ancestors had to decide on the length of a year. Also, they had to decide on the length of a day. As you know a day takes 24 hours. That is the time that Earth takes to rotate once on its axis. A year is longer and takes 365 days. This length of time is related to the time that it takes for Earth to go around the Sun. However, this is not exactly true. Earth’s trip takes 365 days – plus a fraction of another day. This is what complicates our calendar. We have been able to solve this problem by adding an extra day in the month of February. Most often, you will see that February has 28 days. Every four years, February has one extra day. During this year we end up with 29 days in this month. When this happens, the year is called a Leap Year. It helps us keep our calendar in order. Deciding on the length of a month has also been a challenge. Some cultures around the world have used a lunar calendar. A lunar calendar is based on the Moon’s cycle. The Moon takes 29 and one-half days to complete one cycle. Then things got a lot harder. Different cultures start their months at a different time of the Moon’s cycle. For example, the Hebrew and Islamic calendars start their months when a crescent moon is seen in the sky. The Chinese start their new months at the new moon phase. These differences have made it harder for cultures to communicate. Trading with one another has also been hard for this reason. As time went by, most countries began to use the same calendar. When this happened in the twentieth century, trade and communication became a lot easier. Some countries decided to drop thirteen days from their calendar. This is because their old way of counting did not match up with the new way. England had problems with the calendar back in the 1500s. The English decided to divide their calendar into months. Each month had four weeks. By doing this, one week ended up being longer than seven days. Also, this resulted in thirteen months to a yea

3 0

3 years ago

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A titration of 25.0 mL of a solution of the weak base aniline, C6H5NH2, requires 25.67 mL of 0.175 M HCl to reach the equivalenc

Lorico [155]

Answer:

a. 0.180M of C₆H₅NH₂

b. 0.0887M C₆H₅NH₃⁺

c. pH = 2.83

Explanation:

a. Based in the chemical equation:

C₆H₅NH₂(aq) + HCl(aq) → C₆H₅NH₃⁺(aq) + Cl⁻(aq)

<em>1 mole of aniline reacts per mole of HCl</em>

Moles required to reach equivalence point are:

Moles HCl = 0.02567L ₓ (0.175mol / L) = 4.492x10⁻³ moles HCl = moles C₆H₅NH₂

As the original solution had a volume of 25.0mL = 0.0250L:

4.492x10⁻³ moles C₆H₅NH₂ / 0.0250L = 0.180M of C₆H₅NH₂

b. At equivalence point, moles of C₆H₅NH₃⁺ are equal to initial moles of C₆H₅NH₂, that is 4.492x10⁻³ moles

But now, volume is 25.0mL + 25.67mL = 50.67mL = 0.05067L. Thus, molar concentration of C₆H₅NH₃⁺ is:

[C₆H₅NH₃⁺] = 4.492x10⁻³ moles / 0.05067L = 0.0887M C₆H₅NH₃⁺

c. At equivalence point you have just 0.0887M C₆H₅NH₃⁺ in solution. C₆H₅NH₃⁺ has as equilibrium in water:

C₆H₅NH₃⁺(aq) + H₂O(l) → C₆H₅NH₂ + H₃O⁺

Where Ka = Kw / Kb = 1x10⁻¹⁴ / 4.0x10⁻¹⁰ =

When the system reaches equilibrium, molar concentrations are:

[C₆H₅NH₃⁺] = 0.0887M - X

[C₆H₅NH₂] = X

[H₃O⁺] = X

Replacing in Ka formula:

2.5x10⁻⁵ = [X] [X] / [0.0887M - X]

2.2175x10⁻⁶ - 2.5x10⁻⁵X = X²

0 = X² + 2.5x10⁻⁵X - 2.2175x10⁻⁶

Solving for X:

X = -0.0015 → False solution. There is no negative concentrations.

X = 0.001477 → Right solution.

As [H₃O⁺] = X, [H₃O⁺] = 0.001477

Knowing pH = -log [H₃O⁺]

pH = -log 0.001477

7 0

2 years ago

What happens that causes many leaves to change color in the autumn

Alex_Xolod [135]

The pigment that turns leaves green is chlorophyll. when chlorophyll leaves the leaves the leaf will turn different colors<span />

7 0

3 years ago

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Please need help with number 1

Pavlova-9 [17]

One of them is Neatness

6 0

2 years ago

Please help quick the 6th question is “What is a catalyst?” (include all three parts)

allochka39001 [22]

1. The reaction is exothermic.

2. I know this because the delta H is a negative number. (-802.4 kJ)

3. This means that this reaction releases heat.

4 0

3 years ago