Using english to : PREDICT RENDEMEN

1. PREDICT 

DEFINITION :
   
 "  A prediction is a guess what might happen based on observation.And  a statement about what will happen or might happen in the future" 

The Mole Says

  The tips in this section, while helping you to figure out what reaction might occur, aren't infallible in correctly predicting the reaction that will take place. However, if you're not sure what will happen, these tips will be useful in suggesting some possibilities.

An easy way to predict what reaction will take place when two chemicals are mixed is to identify the type of reaction that's likely to occur when the chemicals are combined. Of course, we mentioned before that these types of reaction are arbitrary, but they do sometimes have a useful purpose.

Bad Reactions

   There are two common mistakes when predicting the products of a chemical reaction. The first is predicting the formation of a theoretically impossible product such as NaCO3 or Ag4Cl. The second is failing to balance the equation once the products have been accurately predicted

Here are some tips you may find handy in helping to predict the type of reaction that will occur if you know only the reactants. Keep in mind that not all combiations of chemicals will result in a chemical reaction—these tips are handy only for helping to predict what would happen should they happen to react.

problem 

Problem 4: Write balanced chemical equations for the reactions that might occur when the following reactants are combined:
a) NaOH + H2 SO4 ⇔ ?
b) NH3 + I2 ⇔ ?
c) C3H8O + O2 ⇔ ?

•     If two ionic compounds are combined, it's usually safe to predict that a double displacement reaction will occur.
• If the chemicals mixed are oxygen and something containing carbon, it's usually a combustion reaction.
• If we start with only one reactant, the reaction taking place is probably a decomposition reaction. To predict the products of such a reaction, see what happens if the chemical breaks into smaller, familiar products such as water, carbon dioxide, or any of the gaseous elements.
•       When pure elements are combined, synthesis reactions are the frequent result.
• If a pure element combines with an ionic compound, a single displacement reaction may take place.
• If a compound containing the hydroxide ion is involved, check the other compound to see if it contains hydrogen. If it does, it may be an acid-base reaction.

How to make prediction: 
  
   When making a prediction it is important to look at possible patterns and current observations.

Here are some steps to think about to make a dependable prediction:

• Collect data using your senses, remember you use your senses to make observations. 
• Search for patterns of behavior and or characteristics.
• Develop statements about you think future observations will be.
• Test the prediction and observe what happens.

Example of predict :
  
    Predictions are made in science all the time, but even our daily lives we make predictions every day. Some examples of real world predictions are:

• It is raining and  the sun is out one could predict there may be a rainbow.
• A college student is studying hard for their final exam really one might predict they will get an A on it.
• A child has a fever and a sore throat, one might predict the child has strep throat

2. RENDEMEN

Before performing chemical reactions, it is helpful to know how much product will be produced with given quantities of reactants. This is known as the theoretical yield. This is a strategy to use when calculating theoretical yield of a chemical reaction. The same strategy can be applied to determine the amount of reagents needed to produce a desired amount of product.

Example :

This example problem demonstrates how to calculate the amount of reactant needed to produce a product.

PROBLEM

Aspirin is prepared from the reaction of salicylic acid (C₇H₆O₃) and acetic anhydride (C₄H₆O₃) to produce aspirin (C₉H₈O₄) and acetic acid (HC₂H₃O₂). The formula for this reaction is

C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + HC₂H₃O₂.

How many grams of salicylic acid are needed to make 1000 1-gram tablets of aspirin?

   (Assume 100% yield)

SOLUTION

Step 1 - Find molar mass of aspirin and salicylic acid

From the periodic table:

Molar Mass of C = 12 g
Molar Mass of H = 1 g
Molar Mass of O = 16 g

MM_aspirin = (9 x 12 g) + (8 x 1 g) + (4 x 16 g)
MM_aspirin = 108 g + 8 g + 64 g
MM_aspirin = 180 g

MM_sal = (7 x 12 g) + (6 x 1 g) + (3 x 16 g)
MM_sal = 84 g + 6 g + 48 g
MM_sal = 138 g

Step 2 - Find mole ratio between aspirin and salicylic acid

For every mole of aspirin produced, 1 mole of salicylic acid was needed. Therefore the mole ratio between the two is 1.

Step 3 - Find grams of salicylic acid needed

The path to solving this problem starts with the number of tablets. Combining this with the number of grams per tablet will give the number of grams of aspirin. Using the molar mass of aspirin, you get the number of moles of aspirin produced. Use this number and the mole ratio to find the number of moles of salicylic acid needed. Use the molar mass of salicylic acid to find the grams needed.

Putting all this together:

grams salicylic acid = 1000 tablets x 1 g aspirin/1 tablet x 1 mol aspirin/180 g of aspirin x 1 mol sal/1 mol aspirin x 138 g of sal/1 mol sal

grams salicylic acid = 766.67 g sal

ANSWER

766.67 grams of salicylic acid are needed to produce 1000 1-gram aspirin tablets.

   In chemistry, the chemical yield, the yield of the reaction, or only the rendement refers to the amount of reaction product produced in the chemical reaction. [1] Absolute rendement can be written as weight in grams or in moles (molar yield). The relative yield used as a calculation of the effectiveness of the procedure, is calculated by dividing the amount of product obtained in moles by the theoretical yield in moles

To obtain a percentage yield, multiply the fractional yield by 100%. One or more reactants in chemical reactions are often used redundantly. The theoretical rendement is calculated based on the number of moles of the limiting reagent. For this calculation, it is usually assumed that there is only one reaction involved.

The ideal chemical yield value (theoretical rendement) is 100%, a value highly unlikely to be achieved in its practice. Calculate the percentage of rendemen that is by using the following equations percent rendemen = weight yield / weight of yield divided by the sample weight multiplied by 100%

Example

This is an example of an esterification reaction where one molecule acetic acid reacts with one molecule ethanol, yielding one molecule ethyl acetate (a bimolecular second-order reaction of the type A + B → C):

120 g acetic acid (60 g/mol, 2.0 mol) was reacted with 230 g ethanol (46 g/mol, 5.0 mol), yielding 132 g ethyl acetate (88 g/mol, 1.5 mol). The yield was 75%.

1. The molar amount of the reactants is calculated from the weights (acetic acid: 120 g ÷ 60 g/mol = 2.0 mol; ethanol: 230 g ÷ 46 g/mol = 5.0 mol).
2. Ethanol is used in a 2.5-fold excess (5.0 mol ÷ 2.0 mol).
3. The theoretical molar yield is 2.0 mol (the molar amount of the limiting compound, acetic acid).
4. The molar yield of the product is calculated from its weight (132 g ÷ 88 g/mol = 1.5 mol).
5. The % yield is calculated from the actual molar yield and the theoretical molar yield (1.5 mol ÷ 2.0 mol × 100% = 75%).

References

1. ^ ^a b Vogel, A.I., Tatchell, A.R., Furnis, B.S., Hannaford, A.J. and P.W.G. Smith. Vogel's Textbook of Practical Organic Chemistry, 5th Edition. Prentice Hall, 1996. ISBN 0582462363.
2. ^ Whitten, K.W., Gailey, K.D. and Davis, R.E. General Chemistry, 4th Edition. Saunders College Publishing, 1992. ISBN 0030723736. p.95
3. ^ ^a b Petrucci, R.H., Harwood, W.S. and Herring, F.G. General Chemistry, 8th Edition. Prentice Hall, 2002 ISBN 0130143294. p.125
4. ^ Vogel, A. I.; Tatchell, A. R.; Furnis, B. S.; Hannaford, A. J.; Smith, P. W. G. (1996). Vogel's Textbook of Practical Organic Chemistry (5th ed.). Pearson. ISBN 978-0582462366.